Well it can be compared to L4D in a way but it pre-dates L4D by a fair bit. Humans are all about the point and clicking. Aliens have a more melee based approach with a few specialized aliens such as Onos(tank would be the L4D equiv), Skulk(hunter), Gorge(spitter), Lerk(smoker), and Fade would be like an evolved hunter that could phase through time and space. It boasts a fairly asymmetric play style especially for the commanders. The marines live for the commander, and marine commanding is fairly active. The Hive on the other hand lives for the swarm, and alien commander while still active is like playing an evil gardener raising horrible monsters to kill the humans.