It's well worth the price it's going for nowadays.
I bought it when it came out at $50 and was disappointed w/the value, esp. since Call of Pripyat came out around the same time, only cost $30, and I liked CoP way better (then again, I'm a HUGE Stalker fan, that's why I bought Metro ... but aside from the whole Russian post-apocalyptic thing, it's quite different).
The game it actually reminds me most of is Singularity (although I also preferred Singularity to Metro as well). It's very much a linear shooter with the occasional puzzle situation and a very basic RPG progression. It's bleak, dark, often lonely, and a little bit freaky in parts.
It's not a bad game at all, just not worth $50. As long as you pay under $19.99 I wouldn't think anyone would be disappointed in it.