A lot of the whining this game gets mainly comes from people who treat games like these as fun little timewasters instead of full fledged games, this was never meant to be a replacement for SRB2K like so many people keep insisting (the devs have said that the master server for SRB2K will be kept up) if you wanna play a fun basic MK-Like kart racer then SRB2K is still right there! This game is NOT SRB2K however.

I don't think gating online behind completing (you don't even have to beat it!) a cup is unreasonable at all and the whole "you need 80 spray cans to unlock time trials" is straight up a lie, all you need to do is beat all first page cups with a bronze medal minimum (completely reasonable since you can get all unlocks on any difficulty unless its specified otherwise)
The tutorial WAS pretty terrible since it emphazises too much on mechanics you won't use normally during a race (unless im wrong none of the first page levels have any shortcuts involving the switches, only secrets) and it completely glosses over important mechanics unique to this game like the start position change, tether system, and the drift you can do after hitting a boost panel. I did like the way it was presented though and the interactions between tails and eggman were cute and well written.
There are also some problems with the AI being WAY too rubberbandy, I understand its needed for games like this but sometimes due to the tether system your "rival" in second place can sometimes get an invincibility powerup and theres not really anything you can do to stop them from passing you.
The presentation of EVERYTHING in this game is gorgeous and the amount of love this game has for everything Sonic and SEGA related is incredible (there are entire zones based on levels from fangames!) Just an incredible looking game.

Overall I think with a few tweaks this could easily be one of the greatest kart racers of all time, just hope the devs don't over correct due to all of the mostly misplaced negative feedback.