Ironclad/YMMV

Designated Hero and Designated Villain: The film treats Albany as a hero and John as a villain. Although modern audiences tend to oppose the idea of a divinely-appointed king, by the standard of the times, one can hardly see King John as in the wrong. For example:
 * The opening scene has John being forced at swordpoint to sign the Magna Carta. Signing a document under duress and then deciding not to follow it is not breaking your promise.
 * Under the laws at the time, King John was the legitimate king by right. This was backed by the Pope, who was seen as the highest religious authority. Albany and his men were taking up arms in rebellion against their lawful sovereign.
 * Albany repeatedly claims that the castle belongs to "the people". No it didn't. By law the castle and its lands were the property of the King, to do with as he pleased. Albany had no claim to it, nor did anybody else.
 * Albany also claims that he is fighting for "the people". If by "the people" he meant the tiny percentage of nobles and freedmen who stood to benefit from Magna Carta, then yes. But the idea of a medieval King deriving his powers from the consent of the masses was absurd. It took centuries before the idea of "consent of the governed" came to apply to anybody but the nobility.