Attributes of Jordan's dunk I would say are his legs, he manipulates them in a way while in the air, makes it look better in slow motion. Also like someone else mentions, he leans a lot. Also something about his left hand on certain dunks.
Edit: Pippen style was also somewhat similar to Jordan's. Jordan obviously showed him how to do it his way, which means that perhaps there was some thought behind his style, rather than it just being completely spontaneous. That's just a guess.
Also, when necessary, you see Jordan holding the ball as high as possible, statue of liberty style, on a lot of dunks. Pippen did it as well. I'm not sure why nobody else does that anymore.
It takes giant hands, which isn't to say other NBA players don't have giant hands, but a fair amount of them do not have Jordan and/or Pippen's combination of skill, hand size, and one-foot hops. There's even some big men who've struggled to palm a ball as easily as those guys did. Ben Wallace for instance: http://www.youtube.com/watch?v=DyTRToRIGBM#t=0m31s
When players can palm a rock so easily, that's when you'll get the Julius Erving and Terence Stansbury dunk styles and whatnot. On the flip side, the palming statue of liberty dunks don't always carry the same force and intensity. They can still be strong, but that strength is often stemming more from the wrist than it is the entire arm, something non-palm dunks tend to contain more often.
I think the perfect example of a great dunk that really shows off his style is the Kiss The Rim dunk from Dallas in 1987. The lean and hangtime was ridiculous, and it looked even better in slow motion.