The first game is some of the most fun I've had in a long time, and completely sold me on the 'action' take of tower defense. You can read our full review here, but in a nutshell, we praised the game for its smooth controls, intelligent and dorky sense of humor, impressive visuals, and just all around fun gameplay.
Robot Entertainment is a fairly new developer, raised from the ashes of Ensemble Studios (who most PC strategy fans will recall as the developers of the classic Age of Empires series), and they have cultivated an excellent dialog with their passionate fan base - something they haven't forgotten. Fans of the first game will be rewarded as well, with exclusive unlocks in the sequel for those that own the original.
In short, we can only expect great things from Orcs Must Die! 2. Or, as we at TAL like to call it: Orcs Must Die! Again! Hurray!
Look for our review upon release this summer at theangryluddite.com