I actually thought he was a little over-rated... BUT that is not his fault. I believe the hype / over-hype he received all year was to the level that he could not possibly live up to the hype machine. If you listened to sports talk or watched college basketball sports shows, the on-air personalities were literally wetting their pants and having orgasms about Zion.
When I watched him, I saw a very good player. A VERY physical player. But not sure if he is the type of athlete who is going to dominate the NBA, like he did 17 year old guys. He is not "long". Relatively speaking he is "only" 6'7". For you & me that's very tall. But when you are going up against 6'9" / 6'10" PFs every night, then you are giving up 3-4 inches every game. He also does not have an explosive first step. I think his 1st step is decisive and it is powerful because of his bulk, but it is not "quick". Again, most PFs in the NBA are at least 240lbs, so having a powerful 1st step and bumping into a 250lb body, is a lot different than bumping into a 190lb 17 year old body.