Been playing this with friends since it came out, so gonna give my two cents I suppose.
At first, I loathed the controls. It felt so...foreign. But you know, I got used to them. I even think they're pretty fun now. Of course, once I got better at them, I started to loathe all the other aspects.
In time trials, the game is undoubtably fun. In online multiplayer, it honestly just feels like an exercise in futility. If you fall behind at all, it becomes nigh impossible to ever have a chance at first place again. This is due to many reasons, starting with:
the blue shell being changed to just be avoidable if you're fast enough. On paper, this sounds like a good idea: reward players who are skilled enough with avoiding it, right? In practice, this usually just amounts to not making any overt mistakes, which isn't hard if you're front running away from the pack. This is even further compounded by...
The pack honestly feels like it's even worse than in normal Mario Kart games. You seem to have reduced red shells and such, but fake item boxes have received an even more devastating effect, removing your item and causing an explosion around you. First place is unlikely to hit these due to being alone, but people in the pack are very liable to run into them thanks to power item usage and having to navigate other players, and all it does is serve to keep the pack even further behind. Speaking of...
Power items feel a lot less useful here. Partially because turning becomes impossible when using them, and partially due to track design. Very few tracks even have frequent off road, with many even incorporating a lot of "out of bounds" with, or instead of, off road, and the few that do you're likely to just mess up turns due to how different your handling becomes when using them, and bump into people as well. Which brings me to my next point...
Bumping into people in Mario Kart isn't an uncommon occurrence, but little comes from it. Both players are just shoved to the side a bit, nothing that can't be handled. But in Kart, both players tend to get absolutely catapulted away in opposite directions, completely screwing over both players. Compound that with power items making handling hard, and the pack is frequently screwing each other over.
And you know what? Maybe each of these points wouldn't be as bad, if it weren't for what is possibly the worst sin...
Still using SRB2's server side networking. Even for normal SRB2 no one wants to use it, it's just tolerated because there's nothing better. I get that this is definitely a hard one to fix, but it really shows its faults in a twitch based racer like this.
Also this last one is less of a criticism and more of an inconsistency that slightly bothers me: why does the mega mushroom not give you off road abilities when all the other similar speed enhancing items do?
TL;DR: offline play is fantastic, online play is miserable.