Couple issues I'd like to report.
1. Your displayed keys in the manual for brake and look backward show B and X, but by default when I first loaded the game, these controls are swapped on my controller. I'm using an Xbox One controller if it matters.
2. I ran into an odd graphical issue while choosing a character in the multiplayer setup menu in which a character graphic somehow got super scaled up (to the point where it was bigger than the screen) and sat on top of everything, forcing me to alt+F4 the application. Unsure how this happened specifically, but I had been playing for a couple hours in record attack beforehand. If it matters, bonuschars.kart was added (so I could see how they handled on the graph), and the default resolution was unmodified.
3. The staff replays for MKSC Sky Garden and MKDS Peach Gardens are swapped; attempting to view the replay for one shows the replay for the other.
From what I've played (and I've only played in record attack), it's rather fun, but I can already tell the staff ghosts are going to draw my rage too easily in a number of levels, so if I'm gonna play to relax, I'm probably just going to disable their ghosts and just focus on beating my own times.