I just looked up Megaman on Game Gear on VGMaps.com... (Yeah, it took me this long to bother.)
Wow. Talk about your budget title. It looks like three stages from MM4, three stages from MM5, and then a Wily stage, which is just Quickman's stage from 2. All of the stages are unaltered from the NES versions, with the sole exceptions being that the MEGAMANV letters are (obviously) removed from the MM5 stages. Judging by the maps, it looks like you don't even get to choose your stages. They're presented entirely in "fortress stage" style.
Of course, it's entirely possible the section on VGMaps wasn't complete, but if it *is*... that's pretty sad.