A game system that rewards the player by becoming an "epic" character himself. For example, if you start really small and then slowly build up on your character, unlocking new moves/actions as you do so, then at the end you'll feel epic. If the character was allowed the moves from the beginning on, then it'll feel normal.

So I guess a good evolving of the hero is part of what I'd call "epic". Let him start small so he really feels heroic at the end.