UT2004, is without doubt, the greatest game of all time. It has everything you could even want in a FPS (yes, including vehicles), awesome graphics, and will run on a standard computer.
It has a large variety of weapons and other powerups, lots of gametypes and mutators (add or take or change things in the game), VERY intelligent AI bots, fast and active multiplayer, lots of community support and importantly IT CAN EASILY BE EDITED with the map editor and easy engine to script (like I said there's a lot of support).
I mentioned there is lots of gametypes, here's a list of the built-in ones:
ASSAULT
The idea here is that the attacking team has to get past the defending team's defence to complete objectives. When they finish all they objectives (or the time runs out), sides are switched and the attackers are defending from the defenders who are now the attackers, and have to beat the first set of attackers' time to win (or simply complete all the objectives if they didn't finish).
ONSLAUGHT
A new addition to the UT series; and it involves vehicles :) The aim is to capture power nodes, when you have captured a power node (can be achieved by standing under it and can be sped up by using the link gun on it), the power nodes nearest to it will become available for capture. When you've captured one near the enemy power core, it becomes vulnerable, meaning you can destroy it, thus winning the game. Plays a bit like Battlefield 2 if you've tried that (but obviously better).
DEATHMATCH
Here the idea is to kill as many people as possible, as fast as you can; it helps not to get killed too. The first person to reach the kill limit wins. Or if the game has a time limit, the person with the most kills at the end of the time limit wins.
CAPTURE THE FLAG
The name gives it away a bit. Just a bit. The aim of this gametype is to grab the enemy's flag and take it back to your base, while defending yours. Teamwork is essential here since if the enemy has your flag you cannot capture theirs until it is returned.
TEAM DEATHMATCH
Deathmatch with teams, who would have guessed. One team must kill the other more than they kill them. Works with time and kill limits just like deathmatch.
DOUBLE DOMINATION
Two teams. Two points (A and B). To win your team must capture and hold BOTH points at the SAME time for 10 seconds (variable). To capture a point simply stand on the base. If an enemy stands on the base it reverts to their control, so shoot them before they even get close.
BOMBING RUN
A sort of deadly football. Two teams must fight to get the bomb and chuck it into the enemy goal (or jump in whilst holding it). 7 points for jumping in with it and 3 for shooting it in. To pick up the ball simply touch it; when you have the ball you cannot use any weapons, but can only pass to another player (on your team would be a good idea).
MUTANT
Another unique gametype, and very enjoyable too. At the start it's like a normal deathmatch, but the first person to kill turns into a mutant. After this it's everyone vs the mutant, a bit unfair you may think - but the mutant is almost invisible, very fast, has extra health and full ammo for every weapon (superweapons excluded).
When somebody kills the mutant they turn into the mutant, and everybody has to kill them. Winning works like deatmatch, the first player to reach the fraglimit or the player with the most frags after the timelimit wins.
INVASION
Aha. Invasion. This is a co-operative mode, in which all the players must team up to defend themselves (and each other) against waves of attacking monsters. The monsters are improved versions of the original Unreal monsters. Each wave gets a little more difficult, there are 16 waves but you can change them, and there are mods that can increase the number of waves you can have. You win by surviving all the waves. You lose if all your team dies on a wave.
LAST MAN STANDING
Sort of deathmatch with limited lives. If you lose all your lives (generally about 5 but variable) you lose. The last person to be alive wins. Most certainly a game of survival, as opposed to the normal run-around-shooting-randomly tactics.
VEHICLE CTF
Capture The Flag with vehicles!! This proves to be quite insane, especially on custom maps such as converted CTF-FaceClassic (now VCTF-FaceClassic).
INSTAGIB CTF
This used to be achieved by picking CTF from gametypes, and applying the Instagib (instant kill) mutator. This became so popular that it was made a complete separate gametype! It still uses CTF maps like normal capture the flag. All weapons are removed and you spawn with an unlimited-ammo Instagib Rifle. This is like the Shock Rifle but instant kill and only one fire mode.
There's also many entertaining weapons, which are varied, greatly helping the longetivity of the game. Lots of types of weapon to suit different people.
SHIELD GUN
The melee (close range) weapon of the game. Can be used to attack or defend from oncoming fire.
Primary Fire: Pulverises whatever you touch with it. Hold to charge and make the blast more deadly.
Secondary Fire: Creates a shield around the wielder, blocks fire of all kinds, but runs out of ammo and dissapears if hit too much.
ASSAULT RIFLE
As the name suggests, this is indeed an assault rifle. Fires small bullets and low-damage grenades. Can be used in akimbo (you can have one in each hand).
Primary Fire: Fires a bullet, can't really get simpler than this.
Secondary Fire: Launches a small grenade. Does low damage in a small area. A few of these will easily take a single target out, unfortunately you only carry about 4.
BIO RIFLE
Launches blobs of green (toxic) goo. It can be used to create a temporary minefield or simply to slime a single target.
Primary Fire: Rapidly disperses small blobs of sticky goo. Like I said, this greatly improves the power of a defender.
Secondary Fire: Hold to charge a massive blob of goo. If you hit someone with a large one they will instantly die. If you hit a wall or the floor with a large one it will explode into smaller ones and pepper the area.
SHOCK RIFLE
Now this weapon really does require skill. The two fire modes can be combined for devastating effect.
Primary Fire: Unleashes a small. instant-hit laser. A few shots to kill.
Secondary Fire: Fires a ball of energy, travels quite slow and doesn't really do much damage to the target by itself. But if you hit it with primary fire this all changes; it will explode violently, killing enemies in a large-ish radius.
LINK GUN
Controversial in the ranks of online gamers as a cheap and irritating way of being killed.
Primary Fire: Rapidly fires small plasma stars; these move relatively slow, so it can prove quite difficult to kill someone in open space, although quite effective in narrow corridors.
Secondary Fire: Now here is the annoying fire mode. Releases a constant beam of energy, which does pretty high damage and is easy to keep on somebody no matter how fast they are moving. If you use the secondary fire on your team-mate, it will make their link gun more powerful.
MINIGUN
Bullet firing weapon, very rapid fire but low damage, good for mowing people down in close-medium range.
Primary Fire: Expels huge amounts of bullets in a small amount of time.
Secondary Fire: Like primary fire, but slower rate and the bullets do more damage.
FLAK CANNON
My personal favourite. It's like a futuristic shotgun, and is capable of firing shrapnel chunks or larger exploding shells.
Primary Fire: Launches about 6 small pieces of burning shrapnel in a small spread. Inflicts large amounts of damage.
Secondary Fire: Lobs a flak shell out. This explodes, doing large damage in a small radius and showering the general area with chunks of flak.
ROCKET LAUNCHER
Launches rockets :) Good at blowing up vehicles and bunches of people.
Primary Fire: Releases a single rocket. Can't really say much about it. Small blast radius, average damage.
Secondary Fire: Hold to charge up to 3 rockets. By default they will move in a line, but if you press primary fire before release they will travel in a tight spiral.
LIGHTNING GUN
High power energy rifle. Acts as a sniper that can pierce very thick armour.
Primary Fire: Fires a bolt of lightning. Does about 90 damage everywhere on the body except the head, which is instant kill. Slow rate of fire.
Secondary Fire: Hold to zoom in. Makes killing people from miles away a lot easier.
SNIPER RIFLE
Pretty much the same power as the lightning gun, but looks different (less colourful) and fires bullets as opposed to lightning. Many players favour this over the lightning gun, being good friends with it from the original UT.
Primary Fire: Fires a bullet. Same damage as lightning gun.
Secondary Fire: Zooms in.
MINE LAYER
Deploys spider mines. They sit there doing nothing until an enemy approaches, then the run after them and rip their face off/explode. Vaguely inconspicuous.
Primary Fire: Deploys a spider mine. Chases nearby enemies.
Secondary Fire: You can guide your mines with a laser, they will follow this and kill enemies in the way.
AVRiL (Anti-Vehicle Rocket Launcher)
Launches homing missles that do quite a bit of damage to vehicles; not very good for killing people though, but they can if you hit them dead on. The missiles move quite slow at first, but then speed up.
To lock on to a vehicle, simply hold the crosshair over them for a few seconds.
Primary Fire: Fires the rocket, it will speed up and follow the target it is locked on to, or move in a straight line if you gave it no target.
Secondary Fire: Zooms in on your target and follows it with your view.
GRENADE LAUNCHER
You guessed it. It launches grenades. These grenades stick to people and vehicles, and can be detonated by the user at any time. They will also explode on a timer.
Primary Fire: Launches a grenade.
Secondary Fire: Detonates all grenades (that were deployed by the same gun).
REDEEMER
Launches small nuclear warheads. The most powerful gun in the game.
Primary Fire: Launches a nuke. Travels slowly(ish) in a straight line until it hits something; at which point all hell is unleashed.
Secondary Fire: Launches a nuke, except you can CONTROL IT!!! Move the mouse to move the nuke. This is deadly; although your body is highly vulnerable while controlling it.
ION PAINTER
Targets a huge ion cannon blast. About as powerful as the redeemer but harder to use.
Primary Fire: Hold the laser in one place for a few seconds, and it will target the ion beam which will vaporize everything nearby.
Secondary Fire: Zooms in. Not really necessary but what the heck.
TARGET PAINTER
Works in the same way as the ion painter, except instead of an ion cannon planes come along and nuke the place with mini-redeemers.
Primary Fire: Hold the laser in place like with the ion painter.
Secondary Fire: Zoom in.
In this game there is also things called mutators. These change the way the game is played.
There are quite a lot of mutators supplied with the game, and many people have made many more (including me).
Here are some of the mutators that come with the game:
ARENA
Pick a weapon, any weapon (including custom ones). This replaces all the weapons in the game with the one you chose, and all the ammo with the corresponding ammo type.
LOWGRAV
Does exactly what the name suggests. Low gravity, everything falls slower, whether they are players, vehicles, projectiles or flags.
AIRCONTROL
Lets you set the amount of control the player has over where they move while jumping or falling; the higher the number the more control. Combine with lowgrav for a nice effect.
BIGHEAD
Head size depends on how well you are doing. The higher up you are on the scoreboard the bigger your head, the lower the smaller. Heads can get really big (and easy to hit).
INSTAGIB
Probably the all time favourite mutator of the world. Replaces all the weapons with the InstaGib Rifle. Its basically a shock rifle with only the laser fire mode, except its instant-kill.
VAMPIRE
You gain health when you attack an enemy. I don't know the exact ratio but you can't stand there getting shot and shooting them forever. The reason its called vampire is obvious.
GAME SPEED
Changes the speed of everything in the game. You can change the value it sets it to. 1.0 is normal speed, 0.5 is half speed, 2.0 is double speed etc.
REGENERATION
All players constantly regenerate health.
Combine this with vampire for a challenging(ish) match full of swapping health.
QUADJUMP
Lets you jump four times in one go instead of the normal two. Fun with lowgrav and aircontrol on a deep map.
Those are just examples, there are much more - I have over 500 mutators on my list :D
As I may or may not have mentioned previously, there are indeed vehicles in UT2004. These are available only in Onslaught, Assault and Vehicle CTF (although mapmakers can put them in other gametypes, it just doesn't work too well). Like everything else in the game, the vehicles are brilliant, and are the main difference between this and previous Unreal games.
MANTA
Small one-seater hovercraft. Has a very small amount of health so don't get locked by an AVRiL. Primary fire fires plasma stuff, secondary fire pushes the vehicle fast to the ground, and the jump key boosts it into the air.
SCORPION
Light single-seat ground vehicle. Primary fire chucks out a line of green energy, making a tripline between objects and snares players and vehicles, this can be charged for a longer line. Secondary fire opens blades on both sides of the vehicle, very effective against infantry - simply drive next to a player to eviscerate them; be warned! These blades can be shot off.
HELLBENDER
A rounded three seater ground vehicle jeep thing. The driver doesn't have any weaponry, so teamwork is required if you're planning to do damage with this vehicle. The next seat has a weapon like the secondary fire of the shock rifle. Left click launches the balls of energy and right click blows them all up (like a shock combo) in sequence. The last seat has a laser type thing, primary fire fires a laser (charge for more power) and secondary fire zooms in.
RAPTOR
Flying single-seater craft. Moves very fast and has reasonable armour, good for air-to-air combat and taking out small groups of infantry. Primary fire produces red plasma bolts complete with small splash damage; and secondary fire launches air-to-air missiles, these missiles are homing, but cannot turn very fast so fire straight.
LEVIATHAN
Massive 5-seat ground vehicle. This vehicle is very, very, very slow at getting from one place to another; but it has awesome firepower and amazing armour, excellent for heading a big attack. The driver has a large weapon at his/her disposal, and on secondary fire can convert the whole vehicle into a giant ion cannon. Doing this makes it immobile, but the ion cannon (controlled by driver) has the power of the ion painter - a lot. The other four players in the vehicle have a gun like the second seat on the HellBender, the shock ball one.
CICADA
A two-seat aircraft. Seat one (driver) has the ability to unleash a flurry of rockets onto an area, while primary fire simply fires rockets, secondary fire locks them to a target. The second seat has a laser turret under the craft; primary fire is instant-hit lasers, secondary fire is a ball of light which I'm not sure the effect of, I believe it simply damages stuff.
SPMA
Long range artillery, two seats.
This is a deadly weapon in the right hands; the driver has a huuuuuuge cannon at their disposal, and although it isn't easy to aim the damage and radius are huge. The other seat is the same is the second in the HellBender and the four tertiary ones in the Leviathan.
GOLIATH
Two seater slow moving tank. The driver has your average tank cannon, primary fire launches a high-power shell and secondary zooms; the other seat has a minigun turret, which expels a lot of bullets in a short time - good for taking out infantry, again, secondary fire zooms. The Goliath is very hard to destroy, and average at attacking.
PALADIN
A strange vehicle. It is a large, heavily armoured single seater ground vehicle; it moves at an average speed and is quite versatile. Its weapon is a bright purple laser bolt, and secondary fire puts a plasma shield not all the way around the vehicle but about 90 degrees in front of the turret. It shields against everything I've tried so far.
There are also vehicles specific to certain assault maps, but I don't feel I need to go over them because they aren't used much and besides, this is only a review outlining the key features.
Another feature of this game is Adrenaline. You gain adrenaline by killing people, capturing flags etc; but also by picking up little pills from the floor. When you have full (100) adrenaline, you can execute an adrenaline combo by pressing the correct arrow keys in the correct order. For example: Up Up Up Up for Speed, which temportarily increases the speed of the player, Down Down Down Down for Booster, which continuously regenerates the health and shield of the player. The effects of the adrenaline stop when it is all drained (it is drained while the combos are active).
Now I bring this review to a close. In summary it is a brilliant game with amazing graphics, variety, editability and longetivity. It is VERY addictive, and you will play it for ages if you buy it. A MUST for every gamer.
Most Certainly The Greatest Game Of All Time 
