I enjoyed Moonwalker, but Gain Ground is so damn good! Seriously, if you haven't played it, try it! It's available on many systems such as Genesis, Mega Drive, SMS, PS2 (Japan), and is also an arcade cab. It was part of the Sega Genesis Collection for PS2 (my preferred playing method) and PSP as well as on Sonic's Ultimate Genesis Collection for PS3 and Xbox 360.