The Good

- Introduced the world to Splatoon, Nintendo's first big gamer-centric console IP since Animal Crossing or Pikmin.

- Mario 3D World, Mario Kart 8, Smash, Bayonetta 2 were all well done franchis installments. Star Fox and Pikmin return.

- Nintendo games looked great in HD.

The Bad

- First Nintendo console to have less than 5 years of actual support, really more like 3 1/2 years.

- The worst third party support imaginable. Makes even the N64 third party support look amazing.

- First Nintendo console with no exclusive Zelda game. No Metroid. No real Animal Crossing.

- Terrible software droughts and delay after delay after delay.

The Ugly

- Lowest selling Nintendo home console to date, will end up falling short of the GameCube by millions of units.

- 105 million Wiis to approximately 14 million Wii Us is one of the largest gen to gen collapses in the history of video games.

- The GamePad was never really well utilized in anything but maybe 3 or 4 games total. Epic fail.

Now that it's basically over, what will be the Wii U's legacy in 3-4 years? Is it Nintendo's Sega Saturn? How do you think it will be remembered?

Well, I'd say that on the bright side, WiiU tried to reinvent itself rather than just blatantly be a Wii 2, for better or worse. It had cool gimmicks, like the ability to keep playing even if someone wanted the TV, and some great games overall, like The Wonderful 101, Smash Bros 4, Bayonetta, Devil's Third, Pikmin 3, Fatal Frase and the upcoming Tokio Mirage Sessions (which is shaping up to be good, despite the censorship), to name a few. It also had decent third party support, albeit worse than Wii's.

On the not so bright side, we have an underperforming console whose legacy will definitively taint NX to an extent, and Nintendo's reputation on the market. Say what you want about Sony and Microsoft, Nintendo has been kind of a disaster with the WiiU, more than a virtuous competitor. Not only we have more disatisfied consumers like ever in Ninty's history, we also get a track record of some really horrible treatment to classic IPs (like Animal Crossing), some horrible droughts that relied on nothing but blind hope to get across (or owning another console, yeah), and the fact that the console only lasted a bit more than the original Xbox while arguably having the same (or less!) support overall. 

Not a good heritage, to be honest. NX has a lot to prove.

And still, I know a man who would keep banging the drum and claim it was all part of some grand, genius plan.

Legacy? Its games, but nothing more than that.
Games like Bayonetta 2, Xenoblade Chronicles X, Splatoon and Pokken will make this device become cult among collectors in the future, just like Dreamcast is today.
It could have been so much better if Nintendo wasn´t lazy on marketing/advertisment and on bringing Metroid and Animal Crossing to it. I´m sure a new Animal Crossing game would drive sales of it in Japan, after the huge sucess of New Leaf on the 3ds.

Animal Crossing seems to have been much bigger on handheld than it ever was on console. Guess it just suits portable better.

it will probably be the last traditional console. Every system from here on out will get better hardware revisions

That's an interesting point. Never thought of it that way.

It's legacy will be boosting anticipation for the NX

That´s true. But still,  City Folk sold more than 4.6 million copies, so there´s definetely a good audience for it on home consoles as well.

I think it's legacy hinges on the success/failure of the NX. If the NX fails, then the Wii U will be remembered as Nintendo's first step towards destruction. If it succeeds, then it will probably be remembered as an unfortunate misstep that spawned some great games.