Mushroom Hill is really weird with them; some you'd twist around and run up normally, then you'd have some you run down like in Sonic 4, but for a drastic less length, maybe 96 to 128 pixels of a drop at most, which is pretty much nothing compared to Rush/Sonic 4/Advance games. As everyone says, the only Genesis Sonic stage to really use convex curves in a comparable manner is Stardust Speedway. Convex curves should be level specific, not a level standard. Sonic games are meant to feel like high speed roller coasters a lot, but also remember not every coaster uses convex curves. I'd LOVE to see helix curves in Sonic games more. They only really appeared in Angel Island Zone and Leaf Storm Zone.