The WiiU had a lot of great Nintendo exclusives but the console as a whole was just a mess. The Switch advances on what was a big appeal of the WiiU, off TV console play, with a great year one lineup. My biggest worry is that since year one literally had a good amount of awesome games, year two so far is not looking as good as year one.
All things considered, "I'm worried that they won't have as amazing of a lineup of software in the second year as they did in the first" is not the worst problem to have, coming off the heels of the Wii U...
Also, while Nintendo did make some pretty great games for the Wii U, they never had the one-two knockout punch like BOTW/Mario Odyssey. The Wii U never got a new (non-remake) Zelda game until it was far too late in the console's life, and while Super Mario 3D World was good, it just didn't have that breakout appeal (and stellar marketing and hype) that past bestselling Marios like 64 and Galaxy had, and Odyssey has now. The Switch nailed Nintendo's top tier console franchises in its first year. The only Nintendo franchise that I'd say rivals Mario and Zelda is Pokemon -- and guess what, the Switch is getting that, too!
Mind you, I love the fact that the GCN Zeldas got HD remakes on Wii U (with added second analog stick camera control, so you can't just play the originals on Dolphin and get a unquestionably better experience). And Smash Bros Wii U and Mario Kart 8 are favorites. Games like Tropical Freeze, Bayonetta 2, Pikmin 3, all great. But all that wasn't enough to sell a poorly realized and marketed system, as we saw.