I inherited my C3 SX (2002 Auto petrol) when my granddad was no longer able to dive. It had done around 40K, mostly at 20mph probably. This is my experience so far:
The engine management light was on when I acquired it and it later went into limp home mode. This turned out to be due to collapsed cat and dodgy coil pack. A very expensive fix... The root cause of the which was rain water ingress under the bonnet washer jets. The Citroen garage had no knowledge of the fault even though a quick Google search reveals this is a common fault. Performance was considerably better though with the new cat.
Presently it has a very erratic idle when cold... I'm just waiting for the check engine light and the subsequent hunt the fault game with fault codes.
Handling on corners is pretty bad with the slightest of rain, even when slowed right down the back end feels on the edge of grip. This may be due to the cheap tires that are currently on, waiting for them to need replacing so I can put decent tires on. It's also got quite a large turning circle for the size of car making it not so easy to get out of tight spots.
I do around 400 miles a week of urban, country and motorway driving. Comfort wise it's ok despite the annoying arm rests. Two people and a car set fit in the back ok and there's room in the boot for shopping or a buggy. The rear doors open quite wide which is useful when getting the little one out of the car seat (wide parking space providing).
The C3 seems reasonably willing to accelerate, and even motorway speeds which surprised me, probably because the engine cruses at about 5000rpm at 70-90mph with the 4 speed auto box. I've learned to avoid accelerating too hard below 30mph as it can spend an alarmingly long time between gears when changing down. This is quite hair raising at busy junctions. Overall it changes smoothly given the odd moment of sticking in the wrong gear for slightly too long. At last calculation it did around 37mph.
In short, this model needed a few (hundred) more design iterations to remove basic functionality and reliability flaws, it feels very much like they simple said "this'll do"... Later C3 models might be a bit better, but this experience has tainted my already dim view of Citroen.