Natural Selection 2:
Natural Selection 2 is an immersive, multiplayer shooter that pits aliens against humans in a strategic and action-packed struggle for survival. It seamlessly combines shooter and RTS/strategy gameplay.
Review: 9.3 out of 10 User Score on Metacritic
If you're a fan of online shooters on PC, then Natural Selection 2 not only comes highly recommended, but essential, and should sit right alongside other classic entries into the genre.