So Mario Kart 8 Deluxe is a HUGE improvement over the Wii U version:
1. The graphics are better. I don't know if it's 1080p & upscaling or what, but one of my biggest complaints about Mario Kart 8 was that there was so much going on graphically that it was hard to focus on the game. For me at least, the game is MUCH easier to see & far more clear. I don't know what to attribute this to, other than enhanced resolution & upscaling (I'm playing on a 4K set).
2. The controls are much better. Even simple things like turning are vastly improved. This did a good job fixing this.
3. People in the back actually get good items in the ? boxes now. That was one of our biggest complaints about the Wii U version...once you lost the lead, or being in the upper group, you were just hosed. They fixed that, yay! We actually went back to playing the original Wii Kart game because we were so unhappy with the Wii U version.
Auto-acceleration is definitely nice for kids, as is the option to either tilt the controller or use the joystick for turning. However, after some more gameplay, the single horizontal JoyCon is no good for adult hands, you get cramped after playing for awhile with just a single JoyCon. Hopefully the Pro controllers go on sale for Cyber Monday or something, very curious to test one out!