I have a Sega Genesis now, as of Saturday. I have a few games for it which are mediocre at worst and ok at best (Sonic 2 is probably the best), and I'd go out and get more but I realize I have no idea what games do and do not suck on this console.

Does anyone have any recommendations? Don't worry if someone has already mentioned a title you think is good, I'll treat it as a second opinion.