My favorites were: Kid Icarus: Uprising FF Theatrhythm SFIV Pokemon Rumble Blast Resident Evil: Revelations Tekken Prime Tales of the Abyss Adventure Time! (Love the cartoon lol) Epic Mickey I have a bad taste in games...
If you enjoyed Theatrhythm, you should look into Rhythm Thief. It's a music game that has a pretty interesting story and loads of fun. The tilt games are infuriatingly bad though.
I've only played two games on the 3DS so far: Theatrhythm Final Fantasy, which I did enjoy (and I downloaded the demo to Rhythm Thief too), and Professor Layton: The Miracle Mask, which as with the other entries in the series, was quite challenging (though, I absolutely hate those sliding puzzles where you need to get one thing to the other side around all those blocks).
I probably should have waited to buy mine. I only wanted it for the new smash, the new pokemon, MML3, Monster Hunter 4, and Project X Zone.
Yeah nah, since I got my 3DS I've only played two physical 3ds games. Resident Evil: Revelations and OoT: 3D Both are excellent. Otherwise I have all the ambassador games to keep me occupied along with Pokemon Black.