I think it will be more like the SNES equivilant.. Much like the SNES compared to the NES, the Wii U will have a Stronger library than the Wii (well at least for the core gamer), stronger third party support, better hardware, taking a formula and improving on it, but ultimately lesss success than its predecessor and not as revolutionary.
We can speculate all we want but in the end we really have no idea how the console will perform. There are simply way too many factors to consider (third party support going forward, strength of Nintendo's lineup, state of economy, strength of competitors, etc). It could sell like the PS2 or like the Gamecube for all I know. Now, I lean more towards the former, simply because I find it difficult that a console with many of today's biggest franchises (2D Mario, Zelda, Mario Kart, Smash Brothers, Wii Fit, Call of Duty, Dragon Quest, Monster Hunter), could fail. But who knows..
