Holy ****, just played Natural Selection for the first time.
It's like an FPS version of Alien Swarm with a BF2 Commander role. The guys in there obviously play it a lot as they were calling out locations, weapon types and build trees easily.
So yeah, you build power lines then structures while the commander organises troops and upgrades armour/weapons... all the while the other team are doing the same (marines versus aliens).
Aliens are a varied lot. Skulks are super-fast wall climbers, then there's this scythe-y beast that tears you to shreds. The flying vulture thing lays down clouds of billowing green smoke that causes you damage (as well as obscures your vision) and this GIGANTIC MONSTER RHINO THING causes utter havoc.
It's $35USD and well worth checking out. Still very much in beta though and GoN's server started to lag when we hit 10 players, but on 8 it was as smoothe as a baby alien's eyeskin.http://www.naturalselection2.com/