Graphics.
Really? Yes. The Graphics are the key. If people find that the PS4 and 720 aren't large leaps in appearance for their games, then third-party devlopers will be willing to put their games the same way on the Wii U, because of its iPad style controller, which will and kind of already has people attracted, and also can open up new experiences. With third party support, people will probably choose the Wii U for its first party support as the deal-breaker, primarily because of Nintendo's strategy - of course this isn't confirmed, but Nintendo will most likely release a Zelda game and Super Smash Bros. game for the system around the time the PS4 or 720 come out to lure people and seal sales from its competiters.
Yes, Nintendo's online will be just fine. Here's why. Or rather, hre's two reasons why. Or more. Let me just say some of them here. First, obviously, they have or rather will have most of the features PSN and XBL has (minus the trillion apps that Live has of course), but it will have not only Voice Chat and Text Chat, but more importantly, VIDEO Chat. This will add an extra dimension, but the biggest thing is the introduction of MiiVerse. To be able to seamlessly communicate with friends on your controller's screen to ask for tips, comment on things, share achievements, all while your playing your game, or not.
But lets get back to the point. The graphics are a key point. Of Course graphics don't make hardware, but that was the main thing that caused a lack of third party support for the Wii. If it can hold up to the PS4 and Nextbox, then it's gamepad will look much less than a gimmick, people will choose its first-party games as a deal-breaker, and the Wii U can succeed. Nintendo can get their hardcore audience they want, and their console can lead, for the whole generation, in terms of sales, and respect.
Wii U Pro Controller. When you look at history, Nintendo is pretty much just combining their innovative controllers, not exactly copying the 360 controller.
Available right now on Xbox One and Xbox Series X|S via the EpiXR Game team, Aery - Cyber City is the latest addition to the series.
Dreamland Solitaire: Dragon’s Fury only represents a tiny step forward.
Michael Kitchin writes, "Teenage Mutant Ninja Turtles Arcade: Wrath of the Mutants does not breathe easy outside of an arcade setting. The short campaign loses any risk when you're given plentiful lives at the start of each stage. Whilst the new areas are welcome, they don't make the package feel any more complete. In the comforts of home, every imperfection comes into stark realisation. The slim presentation, the decent but ultimately safe combat and the overall small package makes this tough to recommend."
The Wii's lack of third party support was due to developer stubborness and the Wii controller scheme. The majority of devs put their B-rate and C-rate teams on the Wii while developing AAA games on the HD Twins (I'm looking at you, Ubisoft and EA).
Better grahics are not going to magically bring in the 3rd parties. Gamecube had some of the best graphics in its day, but the worst 3rd party support. Same goes for N64 (it handled 3D MUCH better than PS1 in a lot of cases).
Depends on what you mean by success. If you mean successful for Nintendo (Selling a lot of consoles) then graphics mean nothing. Look at the Wii. If you mean a success to gamers then graphics matter more, because like you said more third-party support + Quality Nintendo's exclusives finally in HD = A Console gamers will consider.
Games and game consoles are about fun and the gameplay aspects. Graphics can be a nice cherry on top, but I will play a game with bad graphics as long as the story is great, the gameplay is sound and if its fun.
On the other hand, I've stopped playing games that had great graphics because it lacked. The Wii U will be successful because people are starved for new hardwar. The Wii U wont be at a graphical disadvantage that many think, the Wii's disadvantage was pretty bad because it wasn't HD. The Wii U is fully HD. Even if the PS4/720 are better graphically, there wont be the difference that we saw this generation.
The controller?
What about the games?