I got to try out the Nintendo 3DS at an exhibition on campus. I just happened to be passing by and I had plenty of free time, so I thought "why not?" I didn't get to use it much, but here's my opinion: its over-hyped.
First of all, it is indeed 3D and no glasses are required, I found that to be pretty cool. You can adjust the level of 3D perspective with a switch and get your preferred setting, I think it looks best with the 3D at maximum level (though I hear this drains the crap out of the batteries). The graphics are also very nice, they seem to be on par with the Nintendo Wii. That being said, it does look 3D but the novelty wears off very quickly. Its kind of like watching a movie in 3D, yeah it looks cool, but after a while I stop caring about it.
I really see that happening with the 3DS. Of the three games I tried (Pilotwings, Street Fighter, and some driving game), the 3D effect really seemed little more than a gimmick. The novelty got old quickly, and really, it didn't even seem "all that 3D" as the commercials would lead you to believe.
That being said, I have a DS and I like it a lot. Honestly, I too was skeptical of the whole "two screens" idea, but in the end I did see that Nintendo stumbled upon genius and it really works for a lot of games. This 3D effect however, I don't get it.