Professor Layton and the Mask of Miracle, originally announced this fall when there was no 3DS, was much better -- and much 3D-i-er -- than you'd expect from a Professor Layton game made for the 3DS. Even though the game still employs the familiar hand-drawn 2D character models, the town map on the bottom screen is now polygonal, and the magnifying glass cursor now zooms in areas of the top screen when you investigate them. It's a nice visual upgrade for the already-pretty Layton franchise. The one puzzle I played, and failed to complete, involved putting a robot together in four parts. The wrinkle was that to assemble it, I had to put the pieces in four boxes, and I had to figure out which box corresponds to which vertical position, and in which orientation. That puzzle wasn't so 3D.
Face Ace was a small demo that started with a photograph of my face (after lining up my eyes and mouth with onscreen lines). It turned that photo into a nightmarish 3D model, dead-eyed and cackling, clad in a weird space helmet. It was up to me to aim a reticle by tilting the DS, and tap to shoot at my own face over and over again.
DJ Hero 3D used the touch screen for the same functions as the DJ Hero controller -- tap to simulate hitting a button, swipe to scratch, and swipe sideways to crossfade. I put it in easy mode for the demo, and that meant that tapping anywhere on the screen activated any color, so it was ... easy. This game had the most noticeable 3D effect of anything on 3DS. The note highway (or whatever you call it) literally seemed to split into two as it hit the bottom of the screen (which means, in 3D terms, that it's flying out directly into your face).
I also played Xevious. It was the classic arcade game, with all the ships and projectiles displaying in 3D. Not really much more to say about that! It is rather interesting that Namco Bandai is experimenting with 3D display for retro games.