Start off nice and simple:
1). No multi scrolling
2). Nothing too complex
3). Initially cater for everyone.
Why not do a puzzle game?
Zoop on the PC/Megadrive/SNES was ok, as were a lot of puzzle games that didn't make it onto Amiga.
Come up with suitable ideas and graphics and music and I will code it for 68oxo Amigas.
So, now that the gauntlet has been laid....... time to start thinking!