Asteroid Base's Lovers in a Dangerous Spacetime! somehow manages to add an interesting new layer to what might be classified a "tower defense" game. Two players operate a circular spaceship, running back and forth between all of the ship's weapon stations to activate the various lasers, thrusters and other devices in an effort to deter hordes of enemy ships.
It's like a platformer inside a space shooter, which is also a tower defense game, and it looks fun to interact with in a way tower defense games usually are not. And it's coming to PC and Mac some time in 2013.