For me the tape/skills don't necessarily match the production. If Mel Kiper etc. had never (largely speculatively) ranked this guy as a top-5 overall player before the season, would you rank him as such from watching him? Not so sure many people would.
He does some things in college that he won't necessarily be able to do in the NFL. For example, a lot of his pressure came from just running around tackles. Of course he'll do that in the NFL (would be idiotic to assert that he won't), but odds are he won't be able to do it anywhere close to the degree he did it in college; he's not going to get to face Xavier Nixon or Mizzou's slow, over-matched RT every week.
He's still a clear 1st round guy and I wouldn't be all that disappointed if the Saints drafted him (well, depending on who's available) but wouldn't exactly call him a steal at 15.