I was a huge fan of Orcs Must Die! 2 when it came out. I knocked a lot of those ornery little buggers off and lost quite a bit more sleep than I had ever intended. The blend of tower defense strategy and third person action really sat well with me, as did the spirit of experimentation. There are just so many delightful traps for proper orc dismemberment, and their upgrades can be a ton of fun.
Plus a look at the new expansion, Garruk's Revenge
I surprisingly high amount of depth makes this trip to the moon worthwhile