Most of what I played was fairly mainstream (your Street Fighters, X-Men, Final Fight, etc.), but probably the most obscure game I was really into was Pig Out, though after trying it again as an adult, I'd say it's more obscure than underrated (it's fine, but nothing that would stand out if you didn't grow up with it). The other one that's coming to mind that I never hear people bring up is Sega's Title Fight, a boxing game that used a twin stick setup so it kind of felt like you were punching when you played it. I haven't tried that on emulation much (last I checked, MAME wasn't rendering the graphics right), so I don't know if it holds up at all.

Most of my gaming is console stuff, even when emulating, so I haven't played that many games on the platform (I really should fix that), but out of the ones I did, it's easily Elevator Action Returns. One of the best action platformers of its era, and a game that should be much better known by the general public.