I've only had the Xantia for a few weeks, so this is really a first impressions kind of review. So far I'm impressed.
The car is very comfortable, although the floaty ride took a bit of getting used to at first. Headroom is a bit limited, I'm 6'0" and my head is only clear of the roof by an inch or so. That said, the car loses some space due to the sunroof, and I sit fairly upright.
The other minor gripe is that the glovebox is miniscule. I do actually keep gloves in it, and there's no room for anything else. Tapes have now been relegated to a box under the seat. The glovebox does boast a light, but it is of limited use as there's not room enough to make things difficult to find.
The car drives beautifully, with good acceleration and handling, although the gears seem a bit short for the engine. The gearbox is nice and positive without feeling clunky, although it is possible to change from fifth to reverse if you're not careful.
The Xantia is generally spacious, with good legroom front and back, and a cavernous boot which happily accomodates a large Great Dane when the back seats are folded flat.
Parking is made easy by having good visibility, a short tail, and power assisted steering.
My last car always seemed to run cool, so the heater never really got going properly. This is not an issue with the Xantia however. The engine gets to temperature within a few minutes, and the heater warms the car efficiently without cooking my feet.
The build quality seems good. Doors close with a satisfying 'thunk' and the car generally feels solid and well put together. The dashboard is well laid out, although there are a lot of warning lights and a couple of them I needed to refer to the handbook to find out what they meant.
To sum up, the Xantia is spacious, quick, and comfortable, and a pleasure to drive.