A good case can be made that michael was not a good Don. Like his brother Santino he was too headstrong, and too aloof be a "good" Don. The two best Dons in the Trilogy are Vito Corleone and Don Tomassino. This is because while both men are very powerful, they never forget where they came from, and they have not only all the necessary Sicilian cunning,and toughness, but they also are kind when they have to be and they create loyalty because they are loved as well as feared. When Vito is hit and when DonTomassino is assassinated, the people who work for them are genuinely despondent.

I also notice that when someone asked Vito for a favor he made a big deal out of "friendship." Other than Enzo the baker, who really did help Michael out, no underling really cares about him
(other than Tom but thats a whole different issue).

Without any semblance of a human touch, Michael was just a brutal, "lousy cold hearted bastard" just like his sister said he was. I mean I don't see Michael going to some local fruit vendor (or small market) and knowing the owner the way Vito did.

Missing that human dimension may be the element of hubris that is the true source of Michael's downfall and the downfall of the Corleone family which even by the end of GFII was already in a state of collapse and as Tom says "once like the Roman Empire."