I like the powerups, and think the way you can power them up is a very nice addition. Sacrificing one item, and slowing down for a bit to power up the other is a cool evolution of the system used in kart racers.
When you find walls you can drive on, it is a really cool feeling, and it goes fine most of the time, but every now and then you slow down while riding a wall. This could be from an opponent shooting you, but it could be the track baiting you into slowing down for a sharp turn. When this happens, you just slowly drift down as everyone passes you. Similar things happen when you go up a trap ramp, or when you hit a bump the wrong way. You just get launched in the air uncontrollably.
When you do, your only option is to reset your car, bringing you to one of many fixed points on the track at a coasting speed. Some might really like it, particularly since you can use it pre-emptively. I found it to be the punishment of your car blowing up, but without the spectacle of the explosion, or satisfaction of others exploding.
I do want to keep playing though, because the thrill is there. I just want to see it more consistently.

Other Notes
- When menuing, there are two accept buttons that are both used regularly, and are not interchangeable. I don't get it either
- Early in the campaign, there's a race that just doesn't end. You cross the finish line, and it just sits at the results screen. No buttons do anything, except pausing (with the usual options). Not a softlock, but it does mean you can't progress in the campaign.
- For some reason, the game randomly changed my camera angle, and there was no option to change it back. Instead of a view behind the car, it put the camera basically on the hood, which was really disorienting when flipping around.
- You can only scroll through the cars one at a time, making it really hard to find specific ones, or compare stats. Basically the same issue Mario Kart 8 has with its vehicle selection.