Mario Kart, mighty gunvolt, Minecraft, splatoon 2 when it comes... There's really a ton of great stuff if you browse the eshop, the Indies are really good if you're into that kinda thing.
Arms is pretty good.
Don't go for Mario Kart since you already have a Wii U. It's difficult to warrant the $60 price for what's 90% the same game released years ago.