I had one (well, I still have it but it's in storage in the garage) and I gotta be brutally honest here: I think it's one of the goddamn worst consoles ever put out that had a relatively normal lifespan (by 'relatively normal lifespan' I mean I'm discounting stuff that flopped so badly it was off the market in 2-3 years and MAYBE at most sold a a couple million consoles but more likely didn't even crack a million).
It was just a failure on practically every level imaginable.
People always talk about the name being why it failed and that obviously was a big reason but there's so much more to it than 'the name was bad'.
Let's talk power real quick: the Wii U was, on paper, a bit more powerful than the PS3 and Xbox 360. Of course in practice, the outdated architecture of the Wii U meant that the few AAA 3P games it got early on (before it became obvious this shit was a flop) often ran worse than on those consoles. It also came out in 2012. The Xbox 360 came out in 2005 and the PS3 came out in 2006. Nintendo released a console that was only a bit more powerful than consoles that were 6-7 years old and at the age where the core gaming audience was getting excited for the next gen of consoles. Outside of hardcore Nintendo fans, nobody wanted to pay $300 for PS360 level hardware with a Fisher-Price tablet controler.
Oh and the library too. Look - I am not going to say 'The Wii U had no goods games', it certainly did have some. But let's be real here: the Wii U came out in November 2012 and that first year-ish of the console's lifespan was brutal. Nintendo clearly thought Nintendo Land was going to be just as an enticing pack-in game as Wii Sports was for the Wii. It wasn't. They probably expected New Super Mario Bros U to be a big holiday hit because it was the first time a new Nintendo console launched with a brand-new Mario game since the Nintendo 64 but uhhh you know launching New Super Mario Bros 2 on the 3DS like four months prior to launching your brand new console (and Mario game) was probably not the best idea. Then Nintendo's next published game (going by US releases here) was Lego City Undercover in March. Again, good game but not exactly something that's gonna make people scramble to buy the Wii U. And it goes without saying that stuff like Game & Wario, Pikmin 3, or The Wonderful 101 were never going to remotely be system sellers.
I'd honestly say the first game Nintendo put out that I'd consider a 'system seller' for the Wii U was Super Mario 3D World.
Which came out in November 2013.
A whole ass year after the console launched . And a whole ass year after the system already became regarded by potential customers as a 'dead system'. You can't come back from that. Plenty of consoles have a slow start at first but the Wii U didn't have a slow start. It literally died out of the gate and the support it got (or rather didn't get) reflected that.
Even the two main selling points of the entire system were at complete odds with each other. The idea was that the Wii U GamePad's display could be used for either second screen functionality like on the DS and 3DS or for playing the game entirely on the controller so someone else can be watching TV instead. But those two gimmicks contradict each other. If a game seriously uses the second screen on the controller then that means you won't be able to use the off-TV play gimmick. But also supporting off-TV play means you can't do anything major with the whole second screen gimmick. (Do y'all remember how Mario Kart 8's GamePad features amounted to 'you can turn on and off tilt controls, display a map, and a fucking horn button' lmao?)
God I could go on but outside of Nintendo's own games, the Wii U was just completely awful in every way possible. Utterly anemic library, underpowered hardware (and it lacked either the cheapness that the Wii had compared to its competiton or a compelling hook that the Switch has comparing to its competition that made people not care about the lack of power), an OS that was slow as molasses (people talk about how boring the Switch and Switch 2 OSes are but I'd rather a console have a boring but snappy OS than an interesting but slow one), a gimmick that never proved itself worth anything, etc.
What a terrible console.
And they can just brick themselves too if you leave it untouched, which is just the icing on the shit cake.