I am currently going through Bioshock and i ain't really impressed 
I mean, even the graphics don't look that great to me. On the other hand, S.T.A.L.K.E.R is one hell of a game. Just like you said, first time i launched the game, i couldn't stop playing it. In 2-3 days i had finished the game which has not happened in the last few years! I mean i didn't gamed a lot these last 2 years. And each and every single players games i played weren't finished in 2 days. It would take me weeks to finish it.
I mean, even the graphics don't look that great to me. On the other hand, S.T.A.L.K.E.R is one hell of a game. Just like you said, first time i launched the game, i couldn't stop playing it. In 2-3 days i had finished the game which has not happened in the last few years! I mean i didn't gamed a lot these last 2 years. And each and every single players games i played weren't finished in 2 days. It would take me weeks to finish it.