Yes, the vast majority of the movie is as historically accurate as Mary Poppins. A militia leader would not have been given the power of Mel Gibson's character. His prowess with a musket is amazing since the musket was only affective within 100 to 125 yards.
Atrocities occur in all wars.
It is the nature of the beast however, the British soldiers in the movie reminded me more of the SS in WW2. The continental forces were not pure and committed their share of atrocities. The uniforms left alot to be desired, especially the British uniforms. The Royal Artillery did not use 20 or 30 pounders in the field as the move depicted. The common artillery piece in the field ranged from 3 to 6 pounds.