The boss at my previous job was pretty horrendous - not really towards me, but towards the company and some of my coworkers.
For starters, I think her biggest problem was inexperience. But, she just also didn't come to the table with very strong ideas and played a lot of manipulative games behind the scenes. She essentially even tried to force out an employee of 12 years because everybody in our building respected him more than her, even though he was by far and away one of the most valuable people in our company.
To her credit, she had a considerable amount of compassion for people going through difficult times (i.e. bereavement) and she was very good with the bottom line, but that in turn meant it would take weeks if not months to replace coworkers who left. It also meant many of us struggling with immense workloads because of her inability to find replacements. I left in mid-September and they still haven't filled my role, and not to toot my horn, but I had a fairly critical role.