All around a fun game. Fun gameplay, with buildings, and bases. Easy to learn, hard to master. Teamwork is essential.
Pros
2 different races (Humans and aliens) which are both extremely different, with different advantages.
Plenty of custom maps.
Bases add a different element to the FPS, making it a cross between a first person shooter, and a real time strategy game.
A credit/Evolve point system based off of kills, allowing you to get stronger aliens/human weapons and armor.
Large community.
Cons
All servers are privately hosted, so you will usually not get good ping.
Graphics aren't all that good.
Game is often swayed by a single, or couple, skilled players who dominate.
The game itself is fairly simple, with only one game type, which is basically destroy the other team, and their buildings.
Both teams have basic buildings, as follows:
A central structure that provides power.
A damaging structure.
A spawn point.
Specific buildings
Humans get an armory, where they purchase weapons with credits, earned by killing aliens; A medistation for healing; and a repeater which provides power outside the reach of the reactor.
Aliens have boosters, which provide poison attacks, and a faster heal rate when standing nearby; trappers, which shoot gobs of black goo that trap humans to the floor for a period of time. Aliens do not purchase evolves, but instead can evolve anywhere, as long as the Overmind is alive.
Both teams advance through 3 "Stages". They start at stage one, and have access to basic evolves/weapons and armor. After a certain amount of kills, the team advances to the next stage, and gains access to more equipment/aliens.
First team to eliminate the enemy base, and all players, wins.