I've heard the top 12 is filled with 1st line potential players, top 6 is elite players. McDavid, Eichel, Hanifin and Kylington supposedly have franchise potential. Not sure about overall depth though... checking out the rankings and some of the players (CHL) in the 2nd round have the same amount of points in their rookie season as players in this years draft ranked out of the top 5 and below... could be as good as 2013 in terms of depth...
This player is ranked 48th, Blake Speers, had same or higher amount of points in rookie season as Perlini, Virtanen, and Bennett
Here's Rankings. http://www.draftsite.com/nhl/mock-draft/2015/