What Harvey said.
I am not a fan of McGinn's own opinion pieces, but I have always respected what he does concerning the draft. It seems that over the years he as managed to gather enough dirt or something on actual team scouts that they are willing to give him rather detailed opinions, and he filters through their conflicting remarks to achieve a combined analysis that has earned him great respect in the media. ESPN and other places refer to his draft pieces quite regularly, and he has won many awards for having the most accurate first round predictions.
As much as I dislike the bulk of McGinn's work, he really shines for a couple weeks before the draft, when he is not using his own analysis but the combined works of an apparently large and quite competent network of individuals who scout the college players for a living.