24 Dollars is almost obscene for that....
It's so good I don't even care that I got in at 50 the day it came out.
If you're looking for more but a bit different, and cheaper, might want to check this out
Killing Floor
It's the same guys who did Red Orchestra, if you're familiar with that
Just an independent group of modders that eventually went retail
UT2k4 Engine, but highly updated
I'm in already