I do wish the Insta-Shield wasn't an unlock relegated to No-Save mode. IMHO Drop Dash should have been down + jump in mid-air. If this is supposed to be a sequel to Sonic 3 and Knuckles, why the hell was the Insta-Shield not a move you had at the beginning of the game? It always felt satisfying to make mincemeat out of bosses with skillful use of it.
Also Blue Sphere is nice, but I still miss the classic gumball machine, magnetic orbs and slot machine bonus stages. Those were really fun.