On the issue of 3DS titles, the Shinobi demo at 3DS was superb. It felt like a Shinobi game. Doesn't look as ugly on the 3DS as it does in screens either.
Super Mario 3DS is also an excellent title from what I've played. Design was a mix of Mario Galaxy and old school Mario platforming.
Sonic Generations....not so sure. If you liked Sonic 4 and Sonic Rush, you'll probably like it, since the physics and game play are kinda similar, though the physics where a bit better.
Mario Kart 7 played like Mario Kart with hang gliders. I've never been a big fan of Mario Kart, but if you like that series....I didn't see much reason to hate it. Unless you don't want more of the same. Personally, I wish SEGA would just put a port of SASR on it.