Blending the two genres together is not even remotely new, but the way it's done here is what makes it special. The Orc enemies come flowing through the map almost like a fluid, and it's down to you to just take out as many as you can, with as many towers and tools as you can handle before they inevitably overwhelm you. The hook is after each round, you go through the vast upgrade tree to boost your stats and gain new towers and then go for another run.
Original Article: link text
Trailer: link text