Well I guess I'm not nuts then. Looking at the game when playing it, something just didn't seem "HD." If you look at the rotating fan blades in track 1 as just one example, they don't look crisp at all. I don't have the greatest TV and I tried moving the sharpness of it around and also moving the Wii U itself back and forth between 720p and 1080i. Nothing worked, but the point is I'd done just because something was noticeably off about how the game looked. Instead of the crazy good AA and sharp resolutions Shin'en was promoting, it looks damned jaggy.
I also noticed slight frame drops on a couple of tracks.
The game does look great and I know Shin'en is a small studio but THEY are the ones who are using the graphics as a selling point. It's fair to point out or be disappointed in the flaws of the visual package.
There's probably some neat graphical tricks I'm not seeing or noticing during gameplay but if they are at the expense of 1280x720 resolution, that's the wrong decision. If there's a track or two they could have made slightly less complex to keep it at a strict 60fps, then that was the wrong decision as well. I haven't progressed to faster speed classes to know if that becomes more of an issue later on, either.
Cool game and worth a purchase for sure. Does it look as good as Mario Kart? To me, no. And gameplay wise, the AI seems a bit unfair at times, physics when jumping sometimes feels goofy, there's a lack of customization (not even changing buttons around), and not much production value outside the visuals. Yes, it's a small file size and that's neat if it's a demo, but there's no true benefit since eShop games don't have size limits this generation.
It's worth a buy but it's not perfect.