While I agree that the bonus should be as-good-as-or-better-than epic, that bonus should only be applicable once the set is completed - or else there is little point to having the concept of sets. Individually, they should be near worthless (in my opinion).
That being said, there is a description on each item of what the set consists of, but not what the benefit is of each set. How do I know which set will be right for me? There needs to be some descption somewhere of what the bonus of each completed set is (and I don't mean on the forum, I mean added to the description of each item).