My dream game would probably be a somewhat-psychedelic-induced roller coaster ride of a 3D platformer taking inspiration from 1920's speakeasies and big band swing music. Structurally it would be like Cuphead (with slightly less of a boss focus) and the artstyle would take heavy inspiration from the bosses in Rayman Legends, and also the cover art of Big Bad Voodoo Daddy's debut album. You'd have a roll button that works like the dash in MMX, but also grants you invincibility during it. If you press the roll button in midair, it's a dive like in Mario Odyssey. There are two kinds of shots you can do with your revolver, one that is activated in the air and shoots downward, which bounces you up a bit and basically gives you infinite jumps (that get continually lower like Kirby in Smash) and one that is activated on the ground and will target enemies and bosses automatically (which you can switch between with the right stick). Movement and physics would be like Shadow The Hedgehog's but good. Every boss (or "crime boss") all have drastically exaggerated features and traits, like the off-duty cop whose torso is in the shape of a donut, or a (comparitively) extremely drunk guy who bears resemblance to Bad Box Art Mega Man and shoots corks from his bottle-top hands.
It's not my fault that it is really easy to write descriptions for these types of stages.