I'll start with the negative points
The explosions aren't very realistic, more 'Hollywood' style.
The physics are a little bit odd. (A tank managing a hit on the opposite side of a ditch without ploughing through the ground first?)
Other than that, Defiance is an excellent film. It is historically accurate with the right weaponry, clothing, acting and language.
It is visually mind-blowing, seeing the individual hairs on Craig's chin as he dodges bullets is an adrenaline rush.
The acting is brilliant, the combination clicks. There's no other way to put it!
Overall, a fantastic film so long as you're not a history buff looking for minor mistakes!