I believe, he is a disciplinarian and doesn't suffer fools. Plus, he has a pretty rigid structure. To an extent he also has a map of how he wants the team to fly. He also demands adherence to his plans. It's his way or highway, as Haller, Anderson, Yarmolenko (I think) are finding out at West Ham. Everyone in the system, know their roles and there's no playing-out-of-the-back-even-when-you-are-[Poor language removed]-at-it nonsense when Moyes is around.

You don't have to be world class to earn your spot, just do your things tidily and you will prosper. Dawson is the latest example. From what I am hearing on WHU boards, they are also impressed by the improvements in Ogbonna / Diop this season.
Even with us, he had pretty solid defensive units across the years: Hibbert / Neville / Coleman at RB, Yobo / Jagielka / Distin / Heitinga / Lescott at CB and Baines (I don't remember anyone else) at LB, none of them world class defenders individually but as a unit you will be hard pressed to find a better/ cohesive defense. If I remember correctly, Stones was also his last acquisition before he left for ManU. So yeah, he understands how to maximize the qualities of whoever he can afford.
That's why I think he IS a good manager who improves the players / system he gets, and not buy the best out there. Of course, he was super defensive while with us, but based on how his West Ham are flying, I suspect it was more to do with Kenwright's shallow pockets rather than his desire and this is not meant as a dig at Kenwright.
Respect....