Graphics:
This was the first Final Fantasy title to be released on the Playstation 2. Square-Enix are well known for their intricate design and explosive production of cinematic FMV or CGI sequences and they certainly took advantage of the PS2s' potential. Cut scenes are seemlessly woven together with in-game graphics, which aids the plotline in its attempt to flow from one 'chapter' to the next.
When the player is free to roam and explore, the environments in which he or she can do so are quite stunning. Again, Square are famous for their mindblowing attention to detail in their backdrops, ever since the release of Final Fantasy 7. There is always something pretty to look at.
The character sprites themselves are impressive, both in and outside of combat. They are fluent in motion, and attractive in detail. A real step up from those used in Final Fantasy 9.

Battle System:
This is probably one of the features that separates this game from previous Final Fantasy titles. The normal ATB (Active Time Battle) system has stepped to the side to make way for a standard turn-based system. This means that instead of waiting for your characters time bar to fill up, you can instantly take your turn straight after the enemy. Its favoured by many over the old system, as it makes for much simpler and quicker battles. The typical skills such as 'Haste' and 'Slow' still have their normal effect on foes, but the new system has allowed them to introduce a new form of obstructing the enemy from attacking. Simple 'Delay' attack skills can be learnt and used to ensure that your other party members can get their hits in before the enemy. A scrollable bar in the top corner of the battle screen allows you to monitor the order of turns. Its even kind enough to show you the effect of using certain abilities, and how it will change the order subsequently. This means you can plan ahead effectively, and it adds more of a strategic element to the battles in the game.
Another huge change is that you can switch characters during a battle. It doesn't take a turn to do so either, so you can keep switching characters until you've selected the character thats of most use to you. Once switched you're free to use an attack with that character immediately. Not only does this add further strategic elements to combat, but it also makes levelling every character much easier than in previous Final Fantasy games. The character merely has to take an action in order to receive the same amount of experience at the end of a battle that all your other characters would.
Fans of Final Fantasy 7 and its 'Limit Breaks' (They were awesome in my opinion) will be pleased to hear that they make a triumphant return after being rendered almost useless in Final Fantasy 8. They are now known as 'Overdrives' and the 'Overdrive Gauge' initially fills up by taking damage. However, as your characters develop, they learn new 'Overdrive Modes.' Setting your characters to different Overdrive Modes will enable them to charge their Overdrive Gauge in different ways. For example, the standard mode 'Stoic' charges a characters gauge when they are attacked. It is much more beneficial for a character that relies on physical attacks to set their Overdrive Mode to 'Warrior' once they have learnt it, as this Mode enables them to charge their gauge by dealing damage to enemies. Overdrive attacks are different for every character, and there are numerous Overdrive attacks for each character. Im not gonna list them all, its up to you to get hold of the game and find them yourself. Overdrives are a big plus point of the game, in my opinion.
Summoning. Whoa. Now this is where it gets interesting. Fan of previous Final Fantasy games? Always wanted to fight as Ifrit or Bahamut? Well now you can, because the guys at Square-Enix are clever people. Yuna, the summoner of the game, obtains 'Aeons' which she can summon, throughout the different stages of the game. Some of the more powerful ones are hidden, but they are definitely worth seeking out. Anyway, once an Aeon is summoned in battle, your characters leave the field, and the Aeon takes their place. Aeons, like your characters, have abilities and skills that you can use in the same way that you use your characters. Later on, you're also able to teach your Aeons whatever abilities you feel like teaching them. Its also worth noting that each Aeon has its own uniqe Overdrive attack. So yeah, awesomeness.
'Trigger Commands' and a number of unique combat situations are also on offer to break up what may, for some, become rather tedious and repetitive battle situations. I don't want to ruin that part, so it'd be best for you to find out some things for yourselves.

Mini Games:
Everyone loves Mini Games. This game has quite a number of them. One of them is actually the acquisition of a new language called 'Al Bhed'. Collecting Al Bhed 'Primers' (There are 26 in total - One for each letter of the alphabet) will help the player to decipher Al Bhed codes and speech within the game, which unlocks various secrets and items.
Blitzball is the main mini game. I won't go into detail about how the game is played, but if you've seen the intro to the game, then you've witnessed the brutality and energy thats associated with it. The game itself is made to look rather complex at first, but once you get the hang of things, its very entertaining, and very rewarding too, if you're good enough. ^^

Longevity:
Oh jesus. I've racked up 300+ hours so far. I still go back to it. And I still start new games just so I can live the storyline experience again. Yeah, maybe I'm sad, but I don't care really, not enough to stop playing this game anyway.
There are monsters on this game that are way harder than the end boss. Monsters with millions of HP and maxed out stats (or close to). So yeah, in order to beat them, you have to rack up full stats, and about 40,000 HP for each character. It takes a LONG time. But its not necessary, so if you don't want to do it, you don't have to.