From my view it was a solid trade. High 1st round pick in a very deep draft for an unproven goaltender with less than 100 games in the NHL, and sub 30 starts in a season. Sure he has lots of potential, but potential doesn't always pan out.
The mistake Gillis seemed to make was in immediately wasting that pick on Bo Horvat when much better prospects seemed to be on the board, but then again I liked Nichushkin at 9th so what do I know.