There's actually a lot of really impressive Wii U games.
Mario Kart 8 still boggles my mind with its beauty, sadly the 720p looks quite bad on my TV (I'd be down for a 1080p remaster on NX, with proper battle mode, of course).
Xenoblade X's scale is just breathtaking. I've put close to 100 hours into it and still find myself stopping to look at the scenery from time to time.
Bayonetta 2 is so stable at 60fps, with wacky shit going on all over the place. Really amazing how much better it performs and looks than Bayo 1 on PS360.
As OP said, Most Wanted is amazing. It was one of the first games that really looked next gen to me, and it still stands up well to the newest racing games on the PS4 and Xbox One.
Last one for me has gotta be Smash 4. It has a shit ton of content, tons of characters, hundreds of songs, and a ton of stages with hazards and whatnot going on, blink-and-you'll-miss-them loading screens (after the first loading screen), all in 1080p, unfaltering 60fps, and up to 8 players at once. The game is a technical achievement, I think you would struggle to get a game to perform like that on any system, let alone the Wii U.