It's interesting that Sony seems to be going for a gaming/phone combo and therefore directly competing with Apple. This leaves Nintendo with the only pure gaming handheld console this upcoming generation (if the rumors about the PS Phone is true, that is).
The big question is if people in general are ready to play serious games on a handheld console. I mean, the iPhone has totally stolen the market the DS began to chew on, and now Nintendo was more or less forced to go back to the gamers who don't want to play simple iPhone games.
It looks like none of its competitors have a 3D-ready handheld yet, but I believe that's only a matter of time. Also, the 3DS' resolution is dreadfully low, actually even lower than the original PSP which came out in 2004... but of course that's because the 3DS can do 3D (which requires the console to render two images at the same time).
If Nintendo can get lots of third party support on board BEFORE Apple and Sony make their own 3D handheld devices, I think the 3DS stands a chance.