I was an exec for two commanders. Not by choice. One was the best commander I ever had and one was the absolute worst. Both of them at the end of the day would pour a glass of scotch and mentor me. Throughout the week they would also call me into their office tell me what they were thinking and ask my opinion. Occasionally I had the opportunity to save the squadron from a morale busting mandatory morning formation run (etc).
Bottom line I learned just as much about how to not be a commander from the bad one as I learned how to take care of people (promotions, assignments, etc) from the good one. I also learned that while I was just flying the line I didn't always have the big picture (and sometimes neither did they as the CC).
The good commander got tired of the BS and left for the airlines. The bad is now an O-6 school dude.