Well I have it installed and running...

Just to give it some contect here is my machine:

Vista Ultimate
GIGABYTE GA-965P-DS3 MB
Intel Core 2 Extreme X6800
CORSAIR XMS2 2GB (2 x 1GB) DDR2 SDRAM
BFG 8800GTX
Western Digital Caviar 500GB 7200 RPM SATA 3.0Gb/s HD

First it takes ages to install, I guess it is seriously compressed to get it all on one DVD.

I got some nasty horrible crash when I tried running it at first. I updated my X-Fi drivers from from the Beta ones to some real ones (came out on the 15th) but no difference. I was using the Beta 101.41 Nvidia drivers. I rolled back to the 100.65 driver and Stalker burst into life...

I have set it to 1920x1080 and Maximum settings (I chose the Maximum setting, I have not gone into advanaced and played with the sliders) and Full Dynamic Lighting. It looks really sweet, the comparison to HL2 era graphics is appropriate. The level are very large by FPS standards but do not think Oblivion or you will really be disapointed... The lighting is fantastic, very authentic, very atmospheric, basically really, really good! Nighttime is properly dark and a thunderstorm at night with the landscape lit convincingly by the lightning flashes is really good. It also has the best implimentation of the flashligh of any game yet (IMO)... Well in those settings with the machine above all runs real well and real smooth...

Combat is not run and gun... Think Ghost Recon with seriously inaccurate weapons... It is difficult to the level of frustrating sometimes, though being RPG I am not sure if I have gotten a bit carried away with picking fights with heavily armed and armoured soldiers... Emptying the clip of your AK into a guys back just to have him trun around and one shot you is frustrating. That is the soldiers, the bandits are considerably weaker.

Remember kids that headshots save lives, usually your own...

The story is difficult to follow and a bit mysterious, but then again I have not gotten that far yet... The main character dialog is in accented english (in my version obviously) and bulked out with further text. Incidental speech is all in Russia which is very atmosphere and adds a challenge too as you can here you enemies calling out to each other but you have no idea what they are trying to do. I spent an additional 10 minutes carefully searching a building for the last bad guy I could hear before i realized it was one of the guys I had put down, he was not quite dead and was calling out (for help I assume)...

I can see where the Fallout comparisons come from, exploring, fighting, looting the corpses, getting frustrated that you can't lug all those weapons around, collecting rare firearms and struggling to find the ammo, mutants wandering around, talking with anyone even though they may not have much to say, radiation bathed post apoloptic landscape... It is all there...

Broken bits... I have not seen the performance issues other Vista users have reported but I have seen a couple of issues that may or may not be Vista related. Firstly CTD with no errors when quicksaving or loading. Not all the time but like 1 in 10. I also saw a CTD once on starting a conversation. Secondly plot holes? I had a mission to save a guy called Carl, I completed it, or at least i think I did, I killed a load of soldiers and escaped a componend with him. He showed me to a manhole and I went on my way... Later after negotiating some tunnels and a small army camp and I escaping on foot to be informed that I failed the mission to save Carl?!?? Have to investigate more...

Overall the strong sense of atmosphere and intense gun fights (getting shot at is as scary as it can be in a game) make everthing else easy to put up with...