I found this game like a bit more than a week ago and have been grinding times. I think it's a great and fun game! It is however a bit unbalanced when it comes to characters. Sonic & Shadow seem to be the same and honestly a bit underwhelming. I think they are at most useful to get used to the game but I am not sure if Knuckles or Tails would do a better job at that.
Knuckles seems fairly balanced, the few times he does excel is probably more fault of unfortunate map design, as in there are a lot big cuts you can take, which honestly is fair game as it slows him down a fair bit usually. There is the cut on 4th lvl (Time city) however thats kind of broken; go straight through the portal at the start, boost as soon as possible, climb up the broken tower beyond the visuals and go for a hard left around the time you reach the end. With some careful glide taps you can reach the skyscraper with the goal emerald (PB: 0:18,433).
Tails is just straight up op if you know what you are doing. Whereas Knuckles benefits from heights, Tails is all about momentum. And oh boy, is momentum exploitable. It's less about the obstacles and more "where do I need to touch the ground, where can I get rings, which boosters can I take, which routes skip the most". If there is any desire to nerf Tails, I'd recommend making checkpoints mandatory. For reference my PBs with tailTails are:
Green city: 0:36,415
Marble Zone: 1:11,564
Casino Night: 1:23:981 (definitely Tails best track)
Time city: ~38 seconds (since overwritten by Knuckles "abuse").
Overall though pretty fun game. Smooth if you download it instead of playing it in a browser. Camera is whatever since most of the time you are boosting forwards anyway (though Casino Night is pretty hard when done the proper way). Playing with a keyboard is perfectly fine. Reset button doesn't work for me (Windows 10). There are 2 platforms in Green city that are not walkable when they should be and just act as not scaleable entities. Would be nice if that got fixed ever.