For those interested, the primary game of Natural Selection is like playing an RTS from a first-person perspective, for the Marine side: one player gets in the Command chair and appropriately becomes the Commander, laying down buildings for the other players to make, making waypoints, researching ugrades that benefit all of the Marine players, dropping health and ammo for them to pick up, etc.
The alien side is much more individualized and is, in my opinion, the more powerful of the two sides, with some really good units and abilities, some of which border on the 'broken' side of things, again in my opinion (particularly the Fade unit). I've found if the Marine players don't finish the aliens off quickly, then the war of attrition generally goes the alien players' way.
I prefer the Combat maps to the RTS maps, where each player is essentially his/her own Commander, researching upgrades for themselves by obtaining points as you kill enemies or are near enough to 'leech' experience from your side killing enemies nearby. The action is fast and furious and usually fun. 🙂
I hope that provides an informative outlook on the game. It's a lot of fun, but like in all games, you'll find people who take the game far too seriously.