First of all, I feel the need to address the rumor I had heard that this movie was nothing like the book. It is true that there are aspects in the movie that weren't in the epic poem, but, as the director points out in the special features, the story had been recorded in writing by monks and was, prior to that, kept only by word of mouth. Given the culture of the Danes at the time, it is highly likely that these monks omitted quite a bit of the vulgarity: the fornication and drunkenness. An attempt was made, during the writing of this script, to add these back to complete the context a bit. Furthermore, the story was changed a bit, as per the Hollywood style, to make the movie more entertaining and acceptable by the current-day audience. So, while literary purists can feel free to continue complaining, Beowulf: Director's Cut does its story far less a disservice than some of the Harry Potter movies, for example, and provides special features that offer a glimpse into why some of theses changes were made.
So, Robert Zemeckis' Beowulf is the story of a heroic Viking adventurer, Beowulf (Ray Winstone), who is accustomed to taming the world's deadliest monsters. Beowulf has heard that Heorot Hall is plagued by a horrible monster, so he and his men venture to the hall, to kill the monster for the glory. The monster, Grendel (Crispin Glover), has proven to be a bane and a curse to the Viking king, Hrothgar (Anthony Hopkins), killing and attacking his people if they sing or make merry. It seems that this is due to the fact that Grendel has very sensitive hearing. As the story progresses, it is revealed that Grendel is, literally, a curse on Hrothgar, as he is the result of the unholy coupling between he and a water demon who had seduced him and tempted him, appealing to his pride. When Beowulf arrives, he sets to the task of destroying Grendel, fighting him in the great hall and ripping off Grendel's arm, assuring his death, but pridefully boasting to Grendel and ensuring that he knew the name of his killer before letting him go. This is a detail that Grendel's mother, the water demon (Angelina Jolie) was quite interested in discovering, as it gave her a target for her vengeance and a good candidate for a lover to give her a new, stronger, son. While Beowulf was a great hero, his greatest weaknesses seem to be vane pride and lust. Thus, like Hrothgar before him, Beowulf becomes king of the land and is quite famous, but, ultimately, is cursed by his earlier actions. His spawn, being of stronger stock, is not a hideously deformed creature, as Grendel was, but is, instead, a magnificent golden colored dragon (also Ray Winstone) who is as beautiful to behold as he is deadly and vengeful. Even though Beowulf talks of his disgust at the Christian concept of martyrs doing away with the heroes of old, in the end, he sacrifices himself to save his queen, Queen Wealtheow (Robin Wright Penn), his lover, Ursula (Alison Lohman) and his people.
The movie adaptation of the story is well written and is well directed. The aspect that makes Beowulf most amazing, however, is the way in which is was created. I had heard that the interesting graphic style of Beowulf was achieved by post processing, in some form of rotoscoping method, much like A Scanner Darkly. This was incorrect, however, although it did look real enough to have been taken from film and then post processed. Instead, the entire film was created using performance capture in a "volume" that was 25' by 25' by 25'. All of the actors' performances were recorded with motion capture techniques. These performances, combined with scanned-in textures of the actors and highly detailed creature models, were used to create a 3D scene inside of the computer. Once the action was set, a cameraman could shoot the same scene over and over, trying different angles until the exact desired effect was achieved. At the same time, since the camera work was done by hand, it felt like camera work from traditional films. Beowulf saw the film-industry debut of a medical technology, Electrooculography (EOG), which measures the most minute changes in eye movement. In Beowulf, this technology is used to capture the subtleties of the actors' eye movements, to bring a new level of realism to performance captured animation.
I would have to suggest that you watch Beowulf once for the story, then watch all of the special features to see how the movie was made, then watch it again to be able to better appreciate how amazing Beowulf actually is. I highly recommend Beowulf: Director's Cut, and look forward to graphic novel movies made with the same cutting-edge technologies it used.