Well,
For Wii U:
-The system isn't cool. Wii branding is dated and passe.
-It lacks the biggest franchises such as GTA, COD.
-It lacks power, and the coolness that comes with that.
-It's marketed to kids, which means kids don't wan it.
-and most of all, core Wii gamers picked up a PS360 and don't see Wii U as an upgrade.
3DS is doing OK, but is being attacked by smart devices.
Nintendo needs to revamp their image and come out with more premium products that kids today want, and adults aren't embarrassed of. They need some western core titles and/or innovative new games that will get great word of mouth as the next big thing. And they should embrace nostalgia and give people systems that remind them of their youth: aka, cool, gamer-focused, powerful, and with adult games and marketing; and possibly labelled NES. No Wii.
