Who says that had a Genesis/Mega Drive and had never played Altered Beast is lying. It is a remarkable game and it was the game cartridge included with the Mega Drive 1 (Here in Brazil, whe had Mega Drive, Mega Drive 2 and Mega Drive 3).
It is very beautiful and challenging game, and it is very identical to the original arcade version. I think SEGA had a great idea of porting their great arcade games to the genesis console.
Basically you are a dead guy raised by Zeus to rescue his daughter. Inside of every stage you challenged by horrible creatures, and has to kill some two headed wolfs to get power-ups that give you power. In each stage the third power-up transforms you into a beast (werewolf, werebear and so...) and in those forms you are more powerful to defeat each boss, that challenge you to a fight at a maximum of 2 times in every stage, those challenges only occur if you are not in the beast form, and in the third time it fights you in your human form if you are ready or not.
SEGA tried to reboot this game for the new generations of gamers, but the game had poorly storytelling and many glitches, and that makes me support this version. Have fun!