I'd actually say Brown was a pretty big riser. He was considered mid to late first round until the U18's.
Having throught about it for a while, the best comparison I can muster for Brown in recent history is Mark Scheifele. Scheifele was even more of a riser, as he was virtually off the map at the start of his draft year. He put up very similar draft-year numbers in the same league, and is also pretty young for the draft. I'd say Scheifele was the slightly better prospect, and that was reflected in his higher draft position, and the fact that he was taken ahead of highly touted players such as Couterier and Hamilton. However, I think reasonable minds could differ on this point.
If Brown ends up like Scheifele, I'd say that Ottawa is happy.