Jordan is a talented big with excellent size and amazing athleticism, but who hasn't really fully developed on either end of the floor and comes with serious limitations.
I've seen him play some excellent defense and be a really good rim protecter (similar to what we've seen from Hibbert, not the same level but similar at times). Other times I've seen him get backed down all too easily for a 7 footer and be late on his rotations, leading to easy buckets. His best upside is on the defensive end though, with his height and ridiculous reach he could develop into a nightmare in the paint for opposing offenses.
He can rebound extremely well, but his frame can let him get outmuscled on occasion if he is out of position.
Offensively he is extremely limited. He has an amazingly high FG%, but that is just a byproduct of the fact that he scores almost exclusively off of dunks from passes from penetrating guards and alley-oops. He has been working on developing a hook shot and some semblance of a game with his back to the basket, but its coming along slowly (if at all). His FT% is abysmal and as a result he is a liability in the 4th quarter because teams will just send him to the line. The real problem is that because of his inability to make shots outside of 3 feet, defenders can sag off of him, which kills floor spacing (at the same time he also gets left open for some easy buckets).
In terms of fit with the Celtics: he could be a really good inside defender if he continues his progression and start using his athleticism to be better on help defense. Offensively he really doesn't bring much to the table, but with Rondo feeding him he could probably improve. He really is a 4th or 5th option on the floor with LAC and only gets the ball when he has his man buried under the basket, but more touches on a rebuilding team might help him expand his repertoire. Rebounding would probably be his greatest addition (especially given the fact that he spend all of his tim in the paint).
At the end of the day he is only 24 and is an amazing athlete. He is certainly overpaid and limited, but he has plenty of room/time to develop and take his game to the next level.