There is nothing else like S.T.A.L.K.E.R.
Nothing.
The game was plagued with a lack of funding and tech. Their vision was unparallelled. You can easily see that with Lost Alpha. The scope was obviously too big for the budget, and yet despite that, they created Shadow of Chernobyl, with measly funding and less than adequate working conditions.
I don't think it needs defended, or warranted a response to "I don't get it." If you "get it", than you do. S.T.A.L.K.E.R. is known as much for being what it wasn't as much as for what it was.
It will always be one of my favorite FPS in life, and it represents the pinnacle of what a single-player FPS can be (to me). It is lonely, haunting, artistically brilliant, and hopelessly flawed. I play through the series at least once a year, and I have yet to be disappointed. Gamers talk about how "story" doesn't apply to FPS. F*&k that. S.T.A.L.K.E.R. has an amazing story, which unfortunately is left vague by the games, even though it's there. I hope the torch is somehow carried by another franchise now that this one is dead, but I've yet to see it materialize.
My advice; if you play this series, take your time. Each kill matters, every shot. Listen to the NPC stories and discover the beauty of "The Zone," and if you are ADHD, don't even bother. The games deserve better than that.