A non-negligible part of the appeal of these games is the slavic-ness of the entire thing. Also Russians and Ukrainians are very prideful, nationalistic (and sometimes a little brainwashed) peoples - misrepresenting them and the STALKER games in this way is sure to result in notable backlash. Which...can often be a good thing for a game's success - drama/ragebait increases exposure and ensures people talk about the game and not some other stupid thing going on like bear sex for instance.
The slavic culture embedded in all three original games was about 50% of their appeal.
Seriously, without that, STALKER would have been another run-of-the-mill sci-fi shooter.
The atmosphere made up for what the games lacked in terms of story.
The Metro series by comparison have a way better plot and graphics, but are linear, and the Russian aspect of them arguably contributed to about 25% of their appeal.
Obviously they're based on legitimate books, but I can imagine an almost identical post-apocalyptic monster zerg taking place in London or New York City.
There have been other nuclear plant meltdowns around the world during the last several decades, but Chernobyl is by far the worst.
Also FYI—one of my relatives was part of the construction crew that reconstructed a new concrete sarcophagus after the old one fell apart.