The problem with Sullinger is that he doesn't really have a great chance of being a star. His absolute cieling is probably Elton Brand, and it has been looking like he might not be athletic enough to even get there (although I do think things could change when he gets with an NBA trainer/dealer).
But, I think there is little doubt that Sullinger will be at the very least a very solid rotation big man, providing he doesn't go on the Michael Sweetney diet. He has great basketball IQ, great ball skills, a good motor, and quick feet for a man his size.
A lot will depend on his measurements, but I think he is also bigger than other undersized big men like Big Baby, Dujuan Blair, Brandon Bass, etc.
Also, a lot of the complaints about him has been about his struggles to get shots off against bigger defenders, but I think this has a lot more to do with the way he is being defended as one of the top players in the country. I think its absolutely a concern if your team is looking for a #1 or #2 option. He will fall short there. However, if you have other options, and just ask him to be a bruiser and rebounder, who can score against single coverage, or pass out of double teams, then he will be just fine.
He has a chance to slide out of the lottery because of the strength of the draft, and his lower upside, but he is an absolute steal in the mid first round, and I would be shocked if he doesn't have a 10 year NBA career, and I expect him to be at least as good as guys like Bass and Blair.