Quality/complexity of the words used to rhyme, flow, charisma, originality.
For example, a lot of Bun B's rhymes are pretty simple ie. smelly red jelly is drippin out ya belly serve em like a deli, jump on my cellular telly... but his flow and the way the words are intertwined makes it dope. Some nerd shit like Paul barnum used really complex rhymes and words, but the shit is wack to me. The MC has to have some of the above traits to be dope, but not necessarily all of them...