Played some games at Comic Con:
New Super Mario Bros U - they only had multiplayer set up which was annoying... 4 players play the game like NSMB, but one extra player uses the tablet to make blocks for your characters to walk on. The girl playing with the tablet had no idea what she was doing and kept on making blocks that ended up getting in my way

Controls seem to be stiffer than NSMB DS...
Pikmin 3 - never really got into this series so had no idea what I was doing. Seems more like a resource management-esque game than anything. Graphics are beautiful, best looking game on the system IMO.
The Wonderful 101 - pretty fun but I don't really like the tablet controller. You have to constantly draw all these shapes on the controller to do moves, and at one point the action switches to the tablet, which is sooo gimmicky.
Rayman WiiU - don't have much experience with the franchise but it was set up for 2 players, one player moves obstacles out of the way with the tablet (and "tickles" enemies to make them vulnerable to attack) and the other player goes through the game like a normal platformer. The guy with the tablet in this one actually knew what he was doing, so it was fun, albeit gimmicky.
Sonic and Sega All Stars Racing Transformed - played on the Panzer Dragoon track with some NASCAR racer person in a Hot Wheels car

Aside from the NASCAR racer inclusion not making much sense (Daytona? getting sales from the vital redneck demographic???) it was cool, with some nice graphics and subtle fanservice. Framerate lagged a but but that was probably because I was playing the 360 version.
Sony Smash Bros - sucked. Very sluggish, simplistic controls, lack of "flow", stupid way to get kills, horrible character roster, no dashing. Everybody was just complaining to the poor rep the whole time "why can't I do x command that I can do in Smash?".
Ni No Kuni - beautiful cel-shaded graphics, lush Ghibli artwork, menu-based RPG, world map, and a whole town filled with armored Boars concluding with a fight against a mechanical Boar??? Yeah, you already know what I think of it.