Anyone try the demo yet? I grabbed it off Xbox Live and gave it a spin. You can pick who you want to play as for a fight between Chuck Liddell and Mauricio Shogun Rua. I tried both, and won two pure striking battles (mainly because I couldn't figure out how to grapple). I beat Chuck by TKO when he turtled up as I punched him, and I beat Rua by knockout (he did a Flair flop).
Was fun. An improvement over the Dreamcast and PS2 UFC games I played long ago. Will be better once I figure out how to grapple. I know the right analog stick is involved, but I'm not quite sure how. Anyway, I'll probably pick this up at some point - it's out May 19th. Don't tell Kane.
I was looking up the release date just now, and Wikipedia tells me that the demo also includes a tutorial to teach you the controls. That might have been handy! I'll give that a try this weekend.
My plan is to wait until the LoZ: Ocarina of Time game comes out for the 3DS (summer 2011) and then buy both the system and that game. I do have the right to change this if the Mario Kart game comes out first though.