The bomber dragonflies and the grabby pterodactyls in RVZ1(OH, AND THE
RING MELTING).
I used to suck at CEZ3, so I still kinda count that.
My friend says the physics can be a bit slippery. I don't really see that, but I
have been playing the game for several years...
The 7th MP special stage, of course. Though somehow I did it
with Sonic on 2.0.
Tails is okay, I guess(he
is my favorite Sonic character...). I used to solely use him in MP, but now I'm just mostly a Vanilla/Mod Sonic player.
Sometimes the spinning fling-things get annoying. I usually have good timing, but...
Azure Temple.
Aerial Garden is surprisingly okay. I got the spade emblem with Fang recently. Somehow.
You can't always get back to where you need to be with certain characters, in certain levels (*ahem*,
Deep Sea).
That's all I can think of. And I've surprised myself by finding things I don't like
about a Sonic (fan)
game.