Warcraft III, and a couple others already did the RTS/RPG one though.
Imagine how hard it would be to come up with a genre. Basically it's not like you officially announce "Okay, I have invented a new genre, the ABCDEFGHIJKLMNOP Genre", you make a game that would fit into several genres, except it's gameplay is so unique that the general public starts thinking of it as having no genre. Then people start making clones of your game, not necessarily bad. Somebody will play some clone and say, "Hey this game is cool" and somebody else will tell them, "Play this one(yours) instead, those other guys just copied off it, it rocks better", and that's pretty much free advertising. Anyway, all those clones bulk up so much that a new genre just comes into being.
Crazy Donut Productions, Current Project: Project Starbuks
Sony stole our name!