The Wii U is a bit too much of a mixed bag for me to deeply appreciate. Yes, it had some very good games, full Wii BC, Miiverse, and occasional good uses for the second screen. But it was also unappealing in a few ways.
The OS was incredibly slow. Switching between different system menus took more than a few ticks, and downloading/installing updates took ages. The build quality of the Gamepad felt a bit below par, with a thin-feeling faceplate, rattling buttons, and unsatisfying button presses. The default battery also drained quickly.
Nintendo put out some memorable games for it (Mario Kart 8, Pikmin 3, DKCTF, Splatoon, Wind Waker HD, Super Mario Maker, BotW, Bayonetta 2, Xenoblade Chronicles X, Captain Toad, Yoshi's Woolly World, Pokkén Tournament), but some felt like 'checking a franchise box' (Super Mario 3D World, Smash), some were just 'there' (Nintendoland, Twilight Princess HD, Tokyo Mirage Sessions), and some were wholly unsatisfying (Star Fox Zero, Mario Tennis, Paper Mario...Animal Crossing: Amiibo Festival -_-). And because of the invisible (even by Nintendo's standards) third-party support, the release schedule for these games always felt like more than a comfortable wait.
But what really put the nail in the Wii U's coffin of notoriety is that, with the announcement of Pikmin 3 Deluxe, the Switch now has a port, sequel, or better franchise installment of just about all the top games I listed (except Wind Waker HD, and Yoshi is debatable), as well as most of the other Nintendo published games. The Switch also feels like a fleshed-out Wii U, being a more portable, more satisfying to use Gamepad. All it's missing is OS features like Netflix, Miiverse, and the internet browser. But I'll take a speedy OS over a packed one, and you're likely to be too busy playing awesome games to care about the missing features much.
The NES had it's faults, but it revived the North American gaming industry, and birthed many industry-defining franchises. And though not a ton of games used it, it was still responsible for popularizing battery-backed saves.