Hopkins is interesting since they have had a very good, and frankly underrated defense the last few years, but they have struggled in net with various players getting time. Ierlan should be a step up, but he's a pretty streaky player - finished last year with a 52% save percentage, but the last four games of the season he was under 50%, including the Ivy League playoff game against Yale when he was 24%. I'm guessing his familiarity with Milliman will help though.
They also lose Mazzone which I think will be a big loss for them as well. He seems like one of those players who is just very hard to replace. If face-offs don't improve (surprised they haven't brought in Blanchard from OSU), I could see them struggling a bit on defense despite improving in goal.