It's whatever we want them to be.
Ideally, we're voting for cards that unbalance the games, but I intentionally left it open for interpretation. I don't want people saying, "But my card isn't too powerful." If it really isn't that powerful, then it won't get a lot of votes. Also, it won't be a big loss if it gets retired. Just looking at the drafts, I can tell that some people value cards much differently than I do. Let's try not to judge.
Addendum:
After completing my first game against Melkor, I vote for his Cursed Scroll.