I thoroughly enjoyed my experience with the Wii U. I skipped the entire first part of Wii U's life until the Killer App for me came out, Smash 4. Smash 4 was actually the first game I've ever pre-ordered (good idea too, since the Gamecube adapter + controller was horrendously under stocked and I got the combo pack) and I've appreciated a lot of games Nintendo gave us for the Wii U. Smash 4 and Mario Kart 8 got a ton of uses on my Wii U. I was still in college when the Wii U came out, and in the spring semester, Friday nights became Smash Brothers nights where we'd pack 13 or so people in my dorm room and we'd just play for hours and hours and hours. Mario Kart 8 is still the best Mario Kart yet and is a huge highlight of owning the console at the time.
Wii U was my first experience with the Bayonetta series, and holy shit, what a great experience that was. Immediately after Playing Bayonetta 1, I had to play it all over again because it was that damn good. Bayonetta 2 was an equally great play-through. Splatoon was an excellent title and had an extremely addicting multiplayer. Pokken Tournament and Hyrule Warriors were great usage of taking Nintendo IPs into new and different genres and both games were pretty excellent at what they did. Can't forget Super Mario Maker, which again, was Nintendo pushing some great creativity to their established IP and giving new experiences that (at the time) you couldn't get anywhere else.
The Wii U was also my experience for some multiplats like Lego Jurassic Park, Tekken Tag Tournament 2, the Batman Arkham Games, Sonic and All-Stars Racing Transformed. So overall, software wise, I was very satisfied with the Wii U. I was completely fine with the Gamepad, it was a pretty comfortable, and it was great for playing games like Hyrule Warriors where I could play it while watching Youtube on my TV, and the Wii U Pro controller is still the best controller Nintendo has ever produced. Seriosuly, the pro-controller is top tier.
My problem with a good chunk for the Switch's software from Nintendo is that it's basically the Super Wii. Mario Kart 8, Pokken Tournament, Donkey Kong Country Returns Tropical Freeze, New Super Mario Bros U were all just Wii U ports with minimum updates. It's incredibly lazy with full $60 price tags. In terms of value, Nintendo is complete shit when they are offering last gen port for one game at full price, while Sony and Microsoft had released entire collections for the same $60 price-tag (Uncharted Collection and Halo MCC).
In a big way, the Wii U forced Nintendo to be creative with their output. No console Pokemon, but instead a Pokemon fighting game. Burnt out from 2D mario? Then make your own. Lack of shooters, especially for the younger demographic? Here's a brand new IP that blew away all expectations. They combined their two biggest exclusive franchises on 3DS and made a completely original and unique game, Tokyo Mirage Sessions #FE, which is another exclusive that I loved. Take something that seemed to be common sense, and make a Zelda themed action game. And while Devi's Third was a failure, it showed Nintendo's willingness to expand to third parties to create exclusive content. This was the same philosophy that they did with the Sega Sonic deal and Bayonetta. Nintendo had to be way more aggressive into making the Wii U unique, which at the time, I think they really did.