Amin Elhassan:
As far as defense, Parker shows good awareness on that end of the court, but he's not very comfortable or confident on the perimeter. His lateral quickness is an issue, and he doesn't seem to know how to effectively use his length and size as a cushion. He also is prone to getting blown by on defense; the same issue bedevils him on closeouts. Parker sags to the paint almost exaggeratedly when playing off the ball, which further complicates his closeouts.
Chad Ford:
However, Parker isn't a slam dunk to be an NBA superstar. He lacks elite athleticism, has some conditioning issues that worry scouts, is a bit of a "tweener" defensively and was torched on the defensive end at times during his freshman season. As big of an asset as he is on the offensive end, he could be that big of a liability on the defensive end.
Parker's ceiling may depend on how much a better conditioning program improves his lateral quickness. He has everything else.