Daaaamn man, the playground had it all. I've seen your comments on how you intended size to be use for getting faster speeds, but you missed so much in my opinion.
I was cruising through each level like "haha, more like, size dOESn'T mAtter" as I was beating them all without adjusting. When I hit the playground and saw the uneven terrain parts I just thought "where was all this?!".
I personally don't want to include the playground as a part of the overall game experience, as it seems more like a dev testing tool, or extra feature. But man, if you added those uneven parts throughout the levels that actually required you to adjust mid race, would be really sick.
Another thing I expected, and honestly the only reason I changed size once, was cause I saw the sand, and the sign saying it behaved differently, so I thought "ahh, this is where we be big, right?" thinking the little car was just gonna get immediately bogged down. Naturally I tested both big and small, and I truly think that's a missed opportunity as well.
Bumps, Tunnels, Jumps, Narrow passages. These could have all drastically changed the use of the theme for the better.
Also the scenery of the playground! It felt so much more alive than the real tracks!
Sorry for the yap, overall great game. Car controls were okay, but it felt a little rubbery, and drifting counter-steered way too aggressively.