My absolute favorite Wii U game is Bayonetta 2 by Platinum Games. The first Bayonetta was one of my favorite games during the previous console generation and this sequel doesn't disappoint at all. In fact, it far surpasses the original in just about every way and I think it's the wildest action game in existence. What's great is that it's a Wii U exclusive and will probably not come out on any other system. Unless, it's a timed exclusive but I haven't heard any rumors to indicate that.
Tropical Freeze was a great game, I'd say that it was a good way to keep our big DK going strong. As for me, Wii U is for playing Super Smash Bros and for the HD remakes. Super Mario Maker is also a jewel among jewels.
Probably Mario Kart 8. I've spent more time on that game than any other on the Wii U by far. Love racing into the wee hours of the night, Roy as my noble avatar. Keep rocking those sunglasses, man.
I also feel like ZombiU doesn't get nearly the credit it deserves. I'd say it's one of my favourite horror-related video games, beating out pretty much all of the Resident Evil titles, and it makes really good use of the game pad.