I've yet a chance to sit down and try one.
I'm not exactly fond of the multi-level of colors with the launch "blue" that they put out. Makes me beg for a see-through replacement shell.
Main game I'm waiting for to play on there, and to know more about, is Saint's Row on 3DS. If it manages to be as good as Saint's Row 2 was (and maybe even have DLC for extra plot/missions), it would be a blast and a half.
I just know that at least for now, if I do get one, I would have to get that Nyko battery pack replacement. ArsTechnica did a review of it and found it more than lives up to its claim of doubling battery life for the handheld; and that's never a bad thing.