A Combination of the following:
- Big, cheap feeling awkward clunky controller that allowed for *sort of portable* gaming but like, not really? Not much of a point..
- Lack of compelling games (hell not just 2nd/3rd party but even from Nintendo!)
- Hurdles of the Miiverse crap to jump through just to get to your games
- Poor marketing (resembled more of a Wii add-on than a brand new console - ran with the Wii branding while many of its games leaned more "hardcore" GameCube style. Iwata even had to tweet a pic of him holding the Wii U informing the public that "yes, this IS in fact a separate console."
- Lack of innovative games that had depth or staying power like Wii Play/Fit/Sports. Nintendoland doesn't really count as it was more a compilation of mini games based on existing Nintendo properties.
My two cents.
I almost see Wii U as a clunky Switch prototype that was clinging to the Wii branding without having much of the spirit of the Wii.
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