I think a STALKER film could be kinda cool ... but I'm not sure how you'd go about showing the mutants, various politics, factions, the massive locale, and the assault into Pripyat and Strelok destroying the device that prohibited further entry into the Zone in a single movie.
And of course if you couldn't show (one of the best scenes ever in a video game IMO) the push through the nature strip in between the adjacent apartment complexes whilst fellow Loner Stalkers yell, scream, cheer and mourn their losses by the time the first movie ended, I don't think it would be that great a presentation..