Alien Breed: Impact, the recently released Team17 game on Steam, was always destined to be a hit. But it would seem that the co-op mode is what everyone is getting all sweaty for.
In co-op mode, players can compete on the Leaderboards and strive for special co-op achievements. Playing as Barnes (a trooper) and Vance (a cargo handler), your job is to locate Conrad; the hero of the singleplayer campaign and their only chance of surviving this catastrophe.
Alien Breed: Impact can be purchased here – http://store.steampowered.com/app/22610
Each purchase comes with a free guest pass allowing a friend to experience the co-op action with you for a full day. If you have already chosen your co-op partner, why not take advantage of the two pack with a 25% discount.