It's essentially a sequel with very different mechanics. Also there's a proper singleplayer campaign with bots, different cups and achievements. It's a bit difficult but I'm having fun with it.
The onboarding is... Pretty rough though. The tutorial is actually half an hour long.
It has waaaaaaaay more mechanics than other karting games. Stuff like fast dropping, spin dashing, like 5 levels of drifting, boosting to pierce shortcut gates... You really don't need to know half of it, but the tutorial does go over everything.
My biggest issue is the amount of buttons and the mapping. Other than that, the tutorial dies di a decent job at teaching the player. I believe there is a way to skip the tutorial but others would have to comment on that.
It's a bit more difficult than most kart racers, yeah. I would recommend the previous one (SRB2K) instead. Super Tux Kart is alright too, probably more fun for kids than for you though. It's very basic.