Wonderful 101 is a minor masterpiece, so much creativity and action and spirit. Plenty of little flaws and a few annoyances that hold it back, but I prefer a little messy and weird but shooting for the stars instead of hyper polish that doesn't try anything new. I also love sentai stuff, over the top shonen manga, kaiju movies, pulp sci-fi, etc., and this game just scratches every itch. Definitely my favorite game on the system and practically a system seller for me. I love Nintendo and probably would have picked up a Wii U at some point anyway, but Wonderful 101 sealed the deal.
Other stuff I've really enjoyed:
Mario 3D World (inventive, funny, surprisingly challenging at times),
Captain Toad (simple but charming and a lot of fun),
Splatoon (got me back into online multiplayer for the first time in ten+ years), the first
Bayonetta (I skipped the PS3/360 generation so this was totally new to me, action-packed and with style to spare), and
Pikmin 3 (my first Pikmin game, so the mechanics were really fresh for me, everything about the game felt so alive and filled with energy, just a pleasure to play).
My gf adores
Yoshi's Woolly World and
Donkey Kong Tropical Freeze; I got annoyed with Tropical Freeze because we played it through co-operative mode and she kept picking me up and throwing me, plus we'd always get separated and the camera would track only one of us, leaving someone to die. I left her to play it on her own, and she claims it's a top 3 platformer of all time, rivaling Mario Bros. 3 and Mario World. I'll return to it at some point and come to my own conclusion, but that's a pretty damn huge statement that I can't see myself agreeing with. There's no doubt it's a well-made game with tons of content. Really difficult, though!
I have Bayonetta 2 but haven't played it yet, that's up next for me.