Ironclad is a movie based (very loosely) on the historical siege of Rochester Caster (1215) by King John of England.
Things it did well:
Showing a siege. Both from attacker and defenders viewpoints and the problems facing both sides including storming/defending the walls, supplies (and lack thereof) and morale. Also, trebuchet! The visuals with these medieval siege weapons were quite well done.
Brutality of medieval combat, no sugar-coating of the combat in this film, blood and gore abounds in the combat scenes with everyone fighting dirty to survive. Unfortunately, there are a lot of quick cuts and shakey-cam usage so it is difficult to actually make sense of what is happening in most of the fights beyond mayhem and bloodshed.
So, if you want to be inspired about running a castle defense (or assault) in your fantasy campaign, give it a look.
Things it did not do well, which you can ignore: