Yay! Really plowing through these partially-started, not-quite finished games at the moment!
Rhythm Thief was excellent. One part Layton, one part Sega Rhythm Game Compilation. Bonkers plot, twists, lots of nice pictures of Paris, clever rhythm games (some of which were somewhat hard!) and some OCD screen-tappage. What more could you want? Apart from the clearly planned sequel, of course.
If you have a 3DS, you MUST buy this. If for no reason other than to tell Sega that this is what we want them making more of rather than shonky Sonic games. You owe it to everyone.