Those tracks can be demanding though; an open cityscape, detailed rock formations, a wide variety of high quality materials from coarse concrete and stone to lustrous metal and translucent ice, weather effects, moving elements like spacecraft and robots. XCX may have a higher quantity of assets in play at once, but FRN's are much higher quality.

Breath of the Wild!

Between Zelda BotW and Mario Kart 8

Zelda BotW for me. Has the best blend of character models, art style, physics, and environment design. It's just a delight to look at.

Runner up would probably be XCX...though only for landscape and scenery. I reeeeeally didn't dig the character models. I remember being terrified of using that black haired loli girl because her model was so creepy looking, and would get mad whenever the game forced me to use her.

And the interaction with these spaces are more than just the size of the track, but interaction with the entire world.

I'm talking about graphics, the quality of the assets/techniques and how good it looks. XCX has some awesome landscapes, but ultimately it has too many visual flaws for it to be a candidate for Wii U's prettiest game in my book.

Based on my experiences, Mario Kart 8.

It can look as great as it wants, if there is no interaction with it, it may as well be a picture.

Except FRN isn't a picture. It's a video game. It has no less interaction than is typical of an arcade racer. And XCX is hardly a paragon of interactivity. Enemies/wildlife do not react to each other, water does not ripple when the player moves through it, cars in NLA pass right through you, foliage does not react when moved through, etc.

So you agree that Breath of the Wild looks vastly better than Xenoblade X?