This is most definitley not your traditional Robin Hood story. It's a dark, intense origin story where Scott has attempted to place the character of Robin Hood in a very real historical context. Though not a true sequel to Kingdom of Heaven, it makes an excellent companion film (sort of the "homefront" to Kingdom's Crusade-set action). The film opens with Richard the Lionheart (Danny Huston) leading his weary army back home to England, sacking French castles on the way. If you're expecting a traditional Robin Hood storyline, Scott dispatches that notion pretty quickly as Richard kicks the proverbial bucket and dies enroute. Robin (Russell Crowe) and his men (Little John - Kevin Durand, Will Scarlet - Scott Grimes, and Allan A'Dayle - Alan Doyle) are lowly archers and men-at-arms in Richard's army. With the king dead, the four decide to strike out for home. But their plans change when the come upon Richard's loyal lieutenant, Sir Robert Loxley (Douglas Hodge - almost didn't recognize him, he played Dr. Tertius Lydgate in Middlemarch), tasked with returning Richard's crown to England. Loxley and his men were ambushed and massacred, and he tasks a reluctant Robin with returning his sword to his father, Sir Walter Loxley (Max von Sydow) in - wait for it - Nottingham. :) Robin & company assume the identity of knights in order to make their way home easier - and of course Robin assumes Loxley's identity.
I'm going to stop with the story recap here (that's probably enough of an introduction, anyway) and delve into the characters and acting for a while. I'll save Robin and Marion for last. :) Back in England Richard left behind a very selfish, immature younger brother - John, played by Oscar Isaac - with serious mommy issues. Eleanor of Acquitaine is played superbly by Eileen Atkins. She's regal and powerful and has a wonderful screen presence - an unexpected jewel of a performance. John is, of course, a disaster in the making, and as soon as the crown settles on his head he goes full steam ahead with his plans to tax, tax, tax. Isaac's performance is interesting and makes you wonder how John would've turned out if he hadn't grown up knowing he was viewed as so obviously the lesser brother. William Hurt makes an interesting appearance as the loyal William Marshal, pushed aside by John for disagreeing with his taxation schemes. Marshal is a rather interesting "bridge" character - thorughly loyal to the crown, he also has a very realistic view of the crown's shortcomings when dealing with its subjects.