After the initial, "He makes weird shootout choices", there really wasn't much to complain about. I questioned his tough love development of young players, but when I saw it actually worked, I trusted him to do the same whenever a young player came in. He implemented a system that was very strong defensively, and strong offensively as well with a by-committee approach.
The numbers speak for themselves since he was here. If you look at the big picture, Bruins were consistently a top team; it's just that the talent of the roster finally caught up to them in the last few years. Best even strength team, top 10 PP, top 10 PK, best defensive team, top 10 offense, and a great analytics team. All things considered, they had a pretty good amount of playoff success as well.
If you aren't completely sick of your coach after 10 years, he's doing something right.