Firingsquad has some more details and screenshots of Alien Swarm Infested:
Alien Swarm: Infested is a sci-fi themed action strategy game with a heavy emphasis on co-op play. It features singleplayer and online modes. As a Commander in the Interstellar Armed Forces, you must guide your squad and successfully complete their mission against the ravages of the Swarm infestation, a threat which plagues mankind across the breadth of colonized space.
Large parts of AS:I's design are intended to encourage the marines to work together. Whether it's singleplayer, with the player commanding all the marines in his squad, or online with each marine directly controlled by a human player, they must work together at all times, or face death at the sharp claws and teeth of the Swarm.