Here's my entree!
Just to keep size of the thread small...
Unlike the special stages of ANY other official Sonic game, this one is trying to make sense (in a way). It is similar to Sonic 2's and 3&K's Special stages, but is on a flat road-like area rather than a pipe or a sphere and has an story/level relation stroner thans Sonic 3's "color-coding". The sketch should explain all by itself, but to make things a little more clear, I'll try to explain one special stage by using Sonic 1's stages. If a special stage is triggered between Green Hill and Marble, then the first part will be in a Green Hill-esque enviroment with loops, rivers and hills in the background, green and brown checker floor, and height-change, bridges and tunnels appearing. Enemys and obstacles would include: Motobugs, totems and Buzzer's bullets to avoid, falling of the bridges and so on. The "boss" would throw spiky balls at the player. After that a Outrun/Super Hang-On-esque change of level-art would ocurr. The trird part would now be purple with sometimes grass on the floor, would have lava and ruins in the background. Tunnels would now appear more often and jumps with lava replace the bridges. Now the player would have to avoid catercillers, Buzzer's bullets and the crushers, not to forget fireballs, coming out of the lava. The "boss" would now try to throw fireballs instead of spikeballs at the player.
The ring-idea could be scrapped with the only goal of parts 1 and 3 being "Get to the (choppa!!) next part alive to face Robotnik!" and rings getting a similar function to those in the stages.
Any questions left? Then PM me and I'll edit this post.
tl;dr: My idea is more awesome then yours, explained with an example