Revenge of the Titans (PC)

2011 was a crazy year for tower defense games.  It seemed like there were a couple of new ones coming out every month, all claiming to have some sort of twist that made them stand out.  Really, though, it was just a bad case of market saturation.  Revenge of the Titans was one notable exception for me during that period.  It had a really great retro charm to it that made the game really appealing, the equipment you could get was neat, and after each map you could assign new projects for your research team to look into  It's a game definitely worth looking into, and there's even a demo, so go check it out. =)