I don't think he's doing a terrible job, I want to make that clear.
And the mistakes in my opinion are 3 main things. Being too conservative at times, clock management, and burning timeouts.
I don't have to give you too many examples about conservative as I'm sure you know a few good instances at the top of your head. ( kicking field goal inside 1 yard line against ATL, punt last week of course) those are just a couple right off the bat.
Clock management is bad on to many occasions. Like when they have the lead in the 4th and they snap it with 15 seconds left on the Play clock. At the end of the half I find it bad for the most part. Except last game as it worked out brilliant.
And the burning of timeouts. He called 2 last week on the Colts final drive because he wanted to see the Colts line up. You just can't do that. If that two point conversation stands, you need to have those timeouts you used. All year he has done that with his timeouts.
That's just my opinion, feel free to disagree of course.
I just think he really has to improve on those 3 main things if the Bills are ever going to be a Superbowl contender one day