Personally for me, I would focus primarily on new zones with interesting mechanics and level design, with only maybe one or two returning zones, both of which not being Green Hill or Chemical Plant respectively. Zone ideas I have include: A lake side, for the first zone. An urban-based area for the second, an amusement park for the next-to-last zone, and a large Egg-Mech inside the park for the final zone, though these are just basic ideas. I'm curious as to what ideas others might have though.
Something akin to Sonic Megamix, just something that can bring back that wonderful feeling of Sonic CD where I think Sonic Mania did a great job imagining what Sonic would be like on the Saturn. Starry Night zone is still a zone I pray will be fully, truly realized in something official, that zone is just too goddamn good to be in a ROM hack that's not seen any updates in a while(again, for good reason.)
Probably something like SRB2, but with non-tank controls and proper 3D polygonal terrain. I would probably add a homing attack in place of the Speed Thok to help with aiming in 3D, though I might just have a jumbo sized Insta-shield to better preserve the flow of the classics and give the homing attack to the flame shield or something.
I would definitely love to make a new 2D game with all new areas and design/animations like Saturn/Mania incorporated. If money wasn't an issue I would have a fairly fleshed out story and feature a few animated cut scenes to help tell the story, in the style of Sonic CD or the Sonic the Hedgehog movie. I'd like to think of it as something like the Sonic the Hedgehog movie but with gameplay in between. Personally I'm a sucker for 2d animated cut scenes and wish more games had them.
