I got the game yesterday and played a couple hours this morning and so far it is great. The graphics I found pretty amazing, the feeling is very nice, only small drawback is that a lot of things seem to respawn, like pesky bandits which you have to kill again and again.
I wanted to try whether I could join the army but it didn't work out that well, I'm now at the Stalker bar(rushed a bit at the start) and I am looking forward to go on next week when I'm back at my PC.

Also using XP makes the whole thing a lot more enjoyable, and for me in Vista it did NOT save the game with the patch applied, it crashed almost every second time, sometimes every time I attempted to save which was rather frustrating, they should fix that.
Another note is, that they actually recommend a DualCore for the game, so all single Core lovers gotta know that the end of their beloved old tech is coming along rather fast(though it's weird they thought about dual cores during development but forgot to optimize it for Vista).