I'd say that what you are seeing is that people are reviewing a game that they expected to be a disaster, yet miraculously wasn't. For awhile it sounded like they were going to destroy the game completely.
Does STALKER have that "Whoa!" potential?
It really depends on what it is that tickles you in a game. I'm probably not the best person to answer this. I noticed you mentioned AAA titles. I don't seem to agree with most people about these sorts of games. For example, I didn't really enjoy Halo or Half-Life. Yet both of those games are considered some of the best games ever made by a lot of people. I tend to classify both of those as "set piece" games. That is, they provide a lot of moments that would probably be at home in a movie. Action packed, and slickly presented. Stalker is very much not like that. It sneaks up on you with what makes it good (at least in my opinion). Little moments that give you a sense of place and environment. Sure, it has it's big moments, but they tend to be big because the game built them up in the interim.
Also, if you are looking for a very story driven game, you might want to pass this one over. Although there is a story, it is not the primary focus of the game. Characters tend to blend into the background. In my opinion, this works out for the best. For example, when I picked over the inventory of a contact I had spoken to just a short while ago... after he had been torn apart by feral dogs. I felt a bit filthy and amoral doing such a thing. Yet I never felt the need to go back to some past save file and rescue the guy. But that was the point. The game gets the idea across that this is not a pleasant place, and it is filled by various people who don't really feel much concern for each other.
Ultimately, if you are looking for an atmospheric game that manages to evoke a slightly earlier style of FPS design, this is it. Plus, you get to explore some really awesome looking underground labs. They really got the look down perfect in those.