To many post to read but this is my take on Doug,
He has one elite NBA skill that is shooting, this alone makes him a first round pick.
Size wise he has solid SF size and below average stretch 4 size. At 6'8 235 with 6'8 wing span. Looking at the draftexpress data base his size is almost identical to Luke Walton and similare to Kyle Singler.
I think Singler is a better skill comp than Walton. Walton was a great passer and role player in both college and the NBA. Singler was a primary scorer in college who is transitioning to a role player in the NBA. Singler is currently averaging 9pts a game in 27min.In college he was an inferior 3pt shooter and FT shooter to mcdermott. His superior shooting should allow him more Korver like shooting numbers and closer to 12pts per game.
Aside from being a spot up shooter I think Dougs intermiadiate scoring game is often over looked. The following article was from last years team USA mini cap.
http://www.sbnation.com/nba/2013/7/23/4551142/team-usa-basketball-camp-doug-mcdermott-gordon-haywardI remember there being buzz on twiiter how well Doug did scoring in this mini camp vs the elite in the nba. This leads me be believe He will be at least a 15pt a game guy in the NBA when playing 25+min
Athletically he is obviously a below average SF and probably average for a stretch 4. This is what will hurt him the most on defense. However smart play and know your teams defense principles can make up for this. This is also predicated on his team having a rim protecting big to help cover his difficencys which the Cs currently lack.
So to answer the question I take Doug with any pick after #9 and would as a rookie expect him to play a reserve role around 20 mpg but still average 10+ pts a game.