So here is a little history of Nintendo's success, small demise, and re-success story. I think that most of us are Nintendo fanboys, just by virtue of growing up in the N64 era. And even though it didn't sell more than the Playstation, we all know it was the better system.
Personally, I love Nintendo for its games. I jumped on the Wii bandwagon, but was ultimately disappointed as the gimmick wore off. I am really curious to see how the Wii U does. Will it re-define gaming like the wii-mote did (motion controls)? I am also curious to play it, because I don't really understand it. With iPads and tablets dominating the mobile market, it makes sense for Nintendo to include touch-screen in their controls, its the new normal. But I am not sure if that will translate well to console gameplay. And it seems to me that casual gamers are becoming less inclined to be tethered to a tv/console, when they can get their fix on an iPhone or iPad etc.
As with all consoles, it will come down to games. If their are good, fun, innovative games, then the console will sell and perform well. If not, then the Wii-U won't sell well. If the latter is the case, then Nintendo will do what it has always done, redefine itself and shift the gaming market.