I know the idea of putting Sonic in a RPG sounds crazy, but hear me out. My ideas are designed to make an RPG that attempts to maintain the trademark sense of speed as much as possible.
-Rating: E10
-Difficulty: Tough, but battles are more about player skill than about leveling up. Some boss fights would require some real clever tactics to defeat.
-Dungeon design: Dungeons would resemble traditional 3D Sonic like levels, but with a camera perspective more like a Tales game to prevent camera based disasters. There would be platforming, but the penalty for falling off a pit would be quite mild, such as some slight damage to the party before you respawn at the start of a platforming section. Each character has a special ability they can use if they are the party leader. Puzzles would involve clever use of those abilities (you'll have to change leaders sometimes). Secret areas of a dungeon or parts of a dungeon you have to revisit later can be explored by using the ability of a party member you got but didn't have at the time you first explored the dungeon.
-Battles: No random battles. Enemies appear in the dungeon normally. If you get a sneak attack on the enemy, you get a first strike on them. The same happens to you if enemies get the first strike. Merely running into enemies does not cause a first strike for anyone. When in battle, the battle system is like something you would see in Tales of Symphonia. Link to example here. Look under gameplay movie 13.
http://www.gamespot.com/gamecube/rpg/talesofphantasia/media.html The reason for this is because that battle system is fast paced, intense, and most importantly, fun. Team Blasts (tribute to Chrono Trigger's team attacks) would exist in the form of a TB gauge. Filling it 1/3 allows for a 2 man Team blast (your controlled character + one partner of your choice. 2/3 full = three man attack (your character + 2 characters of your choice). Full gauge= 4 man Team Blast.
-Characters: Playable characters would include Sonic, Tails, Knuckles, Amy, Shadow, Espio, Omega, Blaze, and Rouge.
-Other: I would intend the game's story to be funny. It would be light hearted, not take itself very seriously, and have some real clever dialouge (even items would have some form of funny or sarcastic description). EXP gain and level ups are fast to reduce the need to grind and maintain fast pacing. The level cap would be up to level 5000.
-Thoughts anyone?