At this point I think most people would agree the Wii U has failed up to live up to the Wii's success. But then the question is, what exactly could Nintendo have done to follow up the success they had with the Wii? How could they reach the Wii's level a second time?

Personally I don't think they could. The Wii seemed very much a one time thing. Nintendo bet on the right technology at the right time and it paid off. They tried it with the Wii U but the technology they bet on was wrong and so it didn't catch on. Nintendo doesn't have a large number of core gamers (who are consistently there to buy consoles/games) to fall back on either like Sony/MS. So ultimately I feel as though it would have been nearly impossible for them to repeat a Wii-like phenomenon because it is like catching lightning in a bottle with the casuals. 

But that's just my opinion. What do you guys think?

Not fail in so many aspects. Like its one thing to not have wii like sales but its another thing to not even have a quarter of that. Nintendo failed with the wiiU in many aspects such as the name, the launch price, the concept, the hard drive space, the technology, the marketing, the pre-launch e3 where they ended the press conference with Nintendoland of all things and not a killer game and the post launch e3 where not only did they not have a regular press conference and the stream itself was laggy. As well as having zero third party support and a giant day 1 update and a 5 hour battery on the gamepad as well as a lack of actual triggers on the controllers and the game delays and the list goes on... The games are great but man, did they fuck up a lot

So there are tons of things Nintendo could have done better and they didn't need to have another wii to make the wiiU successful, they just needed to not fail in so many aspects but they did. The fact that so many people thought the wiiU was a tablet accessory to the wii should already tell you how bad the situation really was

take out the giant controller and you have a system with awesome games for WAY cheaper than the other two.

The Wii was an anomaly. Before the Revolution was announced everyone assumed Nintendo was dead in the water. When Nintendo announced that they weren't competing with Sony and Microsoft everyone scoffed. The fact that WiiSports resonated as much as it did with the mass market was not what everyone expected to happen.

I waited in line at Target to get one...their allocation was extremely low. I asked one of the clerks where the line would begin. They laughed at me and told me there wouldn't be one. They said they'd have plenty of the consoles all month.

So then...the Wii happened. Nintendo took a generation after Sony just destroyed them two gens in a row? What the hell? How did that happen. Erm...it's called the mainstream...which is currently playing on their smart phones, tablets, smart tvs, netflix, etc.

So how again is Nintendo to blame that they couldn't destroy the odds twice in a row? The WiiU actually makes complete sense if you remove the outlier that the Wii was. Nintendo has been losing market share for decades, as companies do when other products are introduced to the market.

What could Nintendo have done to be competitive this gen? Release a tablet/phone and release all their games as free to play with microtransactions. And that's just a world I'm glad never happened.

I feel like Nintendo's woes are as much caused by fanboys enraged by Nintendo's mysterious takeover last gen as with any actual mistakes Nintendo may have made with the WiiU. Go into any gamestop, Target, Walmart, Best Buy and ask the clerk about videogames. These are your ambassadors to your hobby...and every one of them will tell you how terrible Nintendo is and how much better Sony and Microsoft are because they make hardcore, mature games for adults.

A console to follow the creative success of the Wii? It seemed very unlikely to happen, but as a standard console, Ninten could have done well, at least a lot better than it is doing now. There are many problems with the Wii U, such as the name, the tablet, and the POWER. I think the power is holding it back a lot. It just can`t produce what 3rd parties want to do. So of course 3rd parties will abandon it. And the name! I`ve heard a lot of people don`t even know what a Wii U is, and they think the tablet is an accessory. Ninten really goofed up on the marketing. The design could use work. A console`s design is not so important, but it`s got to have at least a decently good looking design. The Wii U is so boring!

If they made a more standard console, like the PS4, or at least match the power of the other 2 consoles, it may have done better. And change that name! Let people know about the console!

Wii U is not the only reason of the current situation. Better Marketing and more games in the beginning would have helped.

The console should've been able to get third party support. Aside Halo and Kart/Smash, nothing boosts HW sales like Destiny/Watch Dogs/Call of Duty/GTA, even when they are bashed by reviewers. This is the main point to me.

Even a more expensive Wii U, like $500, would be in a better situation if it was able to play third party games.

The fact that I like my wii-u 10x more than i did the wii, including said titles like mk6 vs mk8, brawl vs smash 4, dk tropical freeze vs dkcr and even nsmb vs nsmb wii-u, the wii-u has been better to me, that's all that matters.
You ask about the successor to wii-u, well i could care less if Nintendos next systems outsells the Wii, if the titles suck, its a fail.

Wow.  I have read a crapload of posts this last couple of years about the WiiU.  You have absolutely nailed it.

The Wii U had a lot of little problems that ended up compounding, such as lack of third party support, lack of marketing, and a lack of supporting the gamepad.

I'd say a good amount of problems of the Wii U revolve around the gamepad. It was supposed to be the system's gimmick, like the Wii Remotes for the original Wii, yet Nintendo has barely done any interesting things with it, athird parties certainly didn't use it in innovative ways, and it rose the price of the system for no good reason.

The gamepad just didn't catch on like the Wii motion controls, and was pretty much a result of Nintendo trying to directly succeed the Wii.

Well I will just be blunt, it wouldn't have made much difference what they did hardware wise if their launch marketing campaign and first year marketing were as pitifully atrocious as they were with the Wii U. I firmly believe the Wii U would have done better by a noticeable margin with a strong marketing campaign. As for what they could have done better, I think holding off for a year and going for more power (maybe not as much as the PS4 and Xbox One but something closer to get better support and early recognition) while retaining the Wii U's design (shaving some features out of the gamepad to reduce costs would have helped with this) would have improved the fortunes of the system, if you wanted to keep the Wii U's feature set mostly in tact. Most people jump on the name but I'll be frank, Xbox One is a worse name imo.