Natural Selection 2 is a FPS / RTS combo that has you playing in:

The Alien team:

Where you get to be a vicious Skulk who tears everything and anything apart, As a flying creature known as Lerk who spikes marines from a distant so you can go and close the distant for a deadly poison bite to finish off the poor unlucky marine(s), or you can turn in a monstrosity known as Onos, a behemoth who can crush a marine under, destroy Marines structures more quickly than other Alien Lifeforms.

The Marine Team:

Where you build structures for your Commander for him/her to upgrade your arsenal with weapon/armor upgrades, Shotguns, Grenade Launchers or even Jetpack's to catch those Lerks and keep the high ground clear and avoid the onoses hard hits.

This game requires and actually encourages for you to use your microphone to communicate and make tactical moves with your team so if you got a microphone USE IT, trust me you will need it.

The game overall is pretty well done and looks pretty but there are some issues like in every game:

-Net-code problems
-Hit registration
-Unbalanced teams AKA several veterans in the opposite team causing the other team to get entirely "stomped on"

But i recommend that you should get this game BUT only when it's on sale.

11/24/2016 edit:
Playerbase is slowly increasing but surely.

11/23/2017 edit:
Game went 64bit along side 64bit support and has gained a lot of needed and requested fixes/updates, playerbase is still on a steady rise.

11/22/2018
Still receiving needed changes to gameplay, playerbase at a pretty stable rise.