Games. That is one thing we can all agree on. Moveover, enticing exclusive games. All the GTA and CoD ports in the world won't help since people can already play those on a system they own (PS360).
Price Cut - WiiU will sell mainly as a 2nd console for it's exclusive Nintendo IPs. Being so underpowered, and non-casual friendly (casuals don't want a dual analog controller, not even one with a touch screen) it simply won't be a 1st choice for most people. That being the case, it needs to be price accordingly - under $250.
Refocus - Just like the 3D effect of the 3DS proved to be a total bust and Nintendo had to refocus on marketing games instead (and 3D is basically ignored now in marketing) so too will the gamepad be a total bust (for gaming). Nintendo needs to de-empathize that, to the point of making it entirely optional on all games, and market the great exclusive games (well, once it has some).
Functionality - Apps, more multi-media and generally more use for the gamepad (aside from games) since we're all stuck paying for it anyway, it's value must be precieved. If it's not precieved as a worth-while addition to gameplay then it needs to have some other intrisic value added. Being also to play games off of it without TV is great. That's wonderful, but that appeal is limited to the gamer in the family. They need to show stuff that mom will want to use it for too. Considered we all own other touch screen devices with far more Apps than WiiU will ever have, this is a challenge but no other devices currently connect to tv so maybe that can use that to their advantage somehow other than TV/Games.
Mass market appeal games. WiiU still needs it's Wii Sports equivilant (not necessarily a sports game). WiiFit U will fall flat as it's just (from what we've seen so far) adds too little to the Wii Fit formula. Wii owners already own Wii Fit, they aren't going to pay $400 to own it again. Plus the game/fitness craze has long past at this point.
Clear, targeted marketing. WiiU is confusing. To most people it looks like yet another prepherial for Wii. Launching with NSMBU and NintendoLand didn't help cause to the lay person, they look like Wii games. They need to give people a compelling reason to upgrade and clear, concise marketing that this is a diffenent upgrade.
