Flatmate got this massive Sega compilation for his X Box and - after playing Sonic and Golden Axe (naturally), we gave Ristar a go. Nobody had played it before, but it was freakin' awesome!
It's a platform game where you use your hands to grab, climb and kill enemies. The graphics and animation are great, the control is fluid and intuitive and it has a nice 'dynamic'.
Ristar was superb - if I remember correctly it came out quite late in the Mega Drive's life, and so perhaps didn't get the attention it deserved. An XBLA release would be good!