You don't need to have it set on 3D, and some of the games look pretty good...but it all depends on what sort of games you prefer and what make you mainly stood by and enjoyed.
If you love games loaded with great graphics, long storylines, great sound (and now ALSO touch screen) - then NGP.
If you're a die hard fan of Nintendo and have enjoyed there stuff from year dot, you're not particularly bothered by graphics and all the fancy stuff (and are excited for their remakes and ports)..then 3DS (set on 2D). PLUS...it'll be cheaper
You could always purchase the 3DS and see how you feel about it, if it's not something you're really that happy about...trade it in for an NGP when that comes out.