looking over the responses...
a great story: a quest can be non-epic and still have a great story. so a great story alone isn't enough.
power level: (epic-ness?) everything is on a grand scale. summoned gods doing battle vs servant with dagger. this could be a contender.
big / long / hard: big must mean power level / epic-ness, not length. these also seem to be contenders.
immersion, story (again), ambiance, music: games can have all these things and no quests whatsoever - epic or otherwise. so these don't seem to be core components of epic quests, just nice to have.
shine out (uniqueness): it would seem possible to have two similar quests that are both epic, so uniqueness doesn't seem to be a requirement.
high odds. long duration: once again these seem to be common in "epic" quests.
multiple pathways, learning, gaining skills, the unexpected (IE plot twists), an emotional payoff, and a satisfying epilogue are all possible in non-epic quests. so none of those makes a quest "epic". once again they are just "nice to have".
once you strip out the bits that don't necessarily make a quest epic your left with:
grand scale, long time, and high difficulty.
do classic epics pass this test?
are the following epics grand scale, long time, and/or high difficulty?
beowulf
gilgamesh
lord of the rings
the hobbit
the illiad
the oddesy
the golden fleece
the twelve labors of hercules
any other examples?
can anyone name a classic epic that doesn't have at least one of: grand scale, long time, or high difficulty?
can anyone name a non-epic quest that has one or more of these?