I played with the 3DS a lot at PAX East this past weekend. For reference I have a pretty hard time with those 3D glasses in general. The Nvidia keynote at PAX East last year I barely saw anything other than just blurry shit on the screen.
Admittedly the 3DS' 3D effect is pretty incredible. It's a depth 3D and doesn't 'pop out' so to speak. Still it was pretty interesting. The arrow shooting AR game is actually a lot of fun! It's more interactive since you need to move the 3DS around to shoot at stuff. Though it is hard to keep the 3DS in the 'sweet spot' when moving around. It's a good demo of the 3D functionality.
They had some Mii jetpack game or something. I thought that was kinda weak because there wasn't much of a 3D effect at all.
Lego Star Wars had some good depth effects. Dead or Alive was ok, though when you fall onto different stages the 3D effect is pretty stunning.
So like all current 3D technology, you can implement it good (Lego Star Wars) or bad (Mii jetpack game). Really how much you enjoy the game will depend on how much the devs put into the 3D stuff.
I was impressed with the 'technology' of the glasses-less 3D. But after the whole euphoria wore off, I kinda realized, I didn't NEED the 3D to play the game. I was playing with the sliders to see how the 3D effect changed and stuff. I realized all the games work fine without 3D, except the AR games. The AR games were DESIGNED to use the 3D effects, and are an integral part of the gameplay. The others it was more of a 'nice feature' but could be turned off. So ultimately I'm not sure how it'll go with the 3DS in terms of games. I get that you might want the game to work in 2D to reach the broadest audience, but then you lose the entire purpose of having it in the first place.