Good news, the earlier games were certainly buggy, which is a real shame; I haven't played the prequel yet but am currently replaying the original with the complete mod linked recently on this forum, and the game really has some character, I'm having to play it slowly as the difficulty with the mods can be hard enough to make baby jesus cry, but its so different from almost everything out that it's worth playing in it's own right, especially now they finally addressed most of the bugs and increased the performance in the multicore patches.
Can't say I love STALKER, Im kind of two minds on it, but it's definately a great game in it's own right, and I'd still like to give it a play through with Oblivion Lost mod, and also try that early version released recently from the original build.