I'm familiar with the Hero system, and it could work for the setting quite well. However, I shudder at the amount of work involved... I would play in it, but I would never ever run one.
As a game-master, I'm very fond of the Warhammer FRGP system (2nd ed). I'm sure I could make it work...
"I want to be a were-boar!"
"too bad, you're a peasant."