My new favorite game, DEFINATELY worth buying!
About the gameplay, this games features an odd by amazing blend of both First Person Shooters and Role Playing Games, making an apparently simple task like carrying more than 3 machine guns seemly impossible. Don´t get me wrong, this isn´t bad, on the contrary: it gives the game a sense of realism unseen in other FPS. It will force you to sell, buy, exchange and (and this is my favorite one) "harvest" dead bodies in order to get what you want: more weapons, more ammo, more artifacts, and in the end, more money.
But here is the catch (and the answer to why I think this game isn´t perfect): sometimes, ESPECIALLY at the beginning, S.T.A.L.K.E.R. becomes very tedious, making a simple task like killing a bunch of bandits an impossible one. This game isn´t for, say, DOOM fans: you actually have to make an assault strategy in order to win.
The game features, in my opinion, amazing graphics, that are side by side by "overclocking" titan BioShock. Obviously, this will cause some "older" machines to lag, but a simple adjustment in the setups will fix this.
Bottom Line: awesome game, with a few aspects that can be improved.