I used to think Sonic 3 was really easy, but after playing it over Skype with my siblings...
My sister couldn't make it past Hydrocity Act 2, and my brother got to Marble Garden, got a game over on the Act 2 boss, and said "No. This zone sucks and I don't want to play it again. I quit." Then he started playing Binding of Isaac.
The beginning of Hydrocity Act 2 scared the hell out of my sister. She got two game overs there because she kept panicking. lol. Then she would have to fight that tough Act 1 miniboss again.
So, yeah, maybe my perspective of Sonic 3 is colored by how much I've played it and maybe it is kind of a tricky game.
Racing games over Skype or Google Hangout is pretty fun if you get a few friends interested, by the way. Just have everyone broadcasting their game screen.