He's pretty good, but he still needs some work. I doubt he'd be an impact player straight away, but if you're using a late 1st, early 2nd round pick on him, he'd be worth it.
It's hard to judge him based off his play in Australia because there just isn't anyone else his size here (NBL is a guards league). He's freaking huge, and really has no trouble at all getting position in the paint. He really doesn't have any other way of creating offense for himself other than overpowering his opponent. If he's playing in the NBA, he won't be able to do that against every opponent, so he'll have to learn some more ways to score.
I think he would be a great fit for a playoff team that is close (or in Boston's case, there). The game is changing and there isn't as much room for the monsters inside, but in an NBA where everyone else is trying to catch each other, it would be smart to take the lead and add a guy like Jawai who could come off the bench and be a force down low. Just think if the Lakers had a guy like Jawai to knock KG and Pierce around when they went to the hoop early in the series. They would think before they did it again. With Bynum coming back for the Lakers, as well as top teams still having guys like Duncan, Shaq, Yao, Howard, Boozer, Chandler, and perhaps Oden, if you are Boston or Detroit you need to think about that. Even if you are one of those teams with those start players, you still need to think about having some extra beef off the bench.
I just think that Jawai will never be more than a respectable backup, but because of what he could do if he pans out, that is worth a late 1st rounder.