Before going into this movie, you have to forget everything you know about Robin Hood. Personally, I know the legend, but I have never seen the Errol Flynn version, or the Sean Connery version, and I don't think I've seen the Disney version. I may be in the minority, but my favorite is the Kevin Costner version. Prince of Thieves came out when I was 15, and I love the movie to this day.
This movie is a prequel. When we first meet Robin Longstride (Russell Crowe), he is a common archer in King Richard the Lionheart's army. They are returning to London after 10 years of crusades. The king is killed in battle, and Robin and his friends desert. A few things happen, and Robin and his friends return to London disguised as Knights. They end up at Loxley manor, where the widow Marian (Cate Blanchett) and her father in law Sir Walter Loxley (Max von Sydow) live.
There is a lot of setup in this movie. There is a bit about Prince John cheating on his wife with the French King's niece. Prince John becomes King (after Richard's death). John's most trusted friend is Godfrey (Mark Strong), who is sent out to collect taxes. When noblemen aren't able to pay their taxes, their homes are burned and people are killed.
At times, this movie feels more like Kingdom of Heaven or Braveheart. There is a Little John and Friar Tuck, but there is only one scene where they rob anyone. The rest of the movie is about what is going on between the people, the nobles, and the king. Oh, and the King of France is also planning on invading England (with Godfrey's help), which culminates in a big climactic battle at the end of the movie.
Basically this is a prequel to the Robin Hood legend. So don't go in expecting a remake of any other Robin Hood movie. This is the kind of movie Ridley Scott makes better than anyone, and I enjoyed it. I could have done without the subplot involving Robin's late father, though.