"I...AM…BEOWULF" should not be confused with a similarly phrased moment of self-definition in 300. In the latter film, the Spartans were well aware of who they were, when their king announces their nationality with pride. But Beowulf himself is not so clearly defined in his eponymous movie. In fact, Beowulf is just as much about the making of the legend of Beowulf as it is about telling his story.
By the time we meet Beowulf, Hrothgar and his mead hall, Heorot, have already been introduced with examples of the overweening pride that went into Heorot's planning and construction. Grendel has also already made his first appearance, a bizarre creature whose strength and weakness are both to be found in his hearing organ (to call it an ear would insult ears everywhere). And so Beowulf arrives on the scene, seeking nothing more than adventure and the addition of another legend to his name. Beowulf's shallowness and the constantly changing nature of legends is further played out when weaselly Unferth challenges Beowulf's arrogant demeanor: the most definitive story about Beowulf involves him losing a swimming race, and Unferth wonders why the safety of Heorot and its people should be left to a man who cannot even win one. Beowulf responds by telling "the real story" of the swimming race, of how he had been attacked by sea monsters and fought them off along the way. Ironically, the images on the screen do not reflect the story Beowulf tells; he claims he could've caught up and won the race if the last monster had not entrapped him, but the audience sees images of him being seduced by a mermaid. This metafictional moment highlights two recurring issues for Beowulf: his legend is bigger than the truth, and he is a very lusty man. After the swimming story is finished, Beowulf's companion Wiglaf responds to the reputed death of nine monsters with the comment that at the last telling there were only three.
Even when Beowulf fights Grendel and the story is eventually retold, elements of it are expanded to aggrandize Beowulf. As the fight takes place, it's clear Beowulf has some skill, but he also has luck on his side. Beowulf takes advantage of nearby tools to tear off Grendel's arm, and when this later scene is retold, the story is that Beowulf tore off his arms with his bare hands.
But even in his greatest moment, Beowulf suffers from his own debilitating lust, both for fame and for the female form. When Beowulf pursues Grendel's mother into her lair, she offers him eternal fame if only he will sire a new son for her. Of course, she appears enchantingly beautiful to him and he cannot resist either offer. And so the circle starts over, this time with Beowulf as king rather than Hrothgar.
Throughout the movie, Beowulf is promised long-lasting fame beyond his actual accomplishments and it's clear that, picking up the metafiction again, he achieves it since the story taught in our classrooms is greater than the story of the movie: by the fiction of the movie, Beowulf's legend has outgrown the truth.
You'll notice by now that I don't talk about the actors or the cool new element, the 3-D animation effects. To be honest, except for the moments when the movie's creators demand that you see the 3-D effects (like a spear coming directly at your face), the 3-D isn't all that important. Director Robert Zemeckis establishes the beauty and possibility of his new toy early on, but then goes about telling his story. This is the inherent flaw with new cinematographic effects—unless those effects become characters in the movie, they have to take a backseat to the story being told. A successful use of the new technology means that the viewer accepts it and moves on, and this is the case with Beowulf. It's only afterwards that one can really appreciate how layered each shot is, because the Beowulf story itself is so engaging, especially with the metafictional twists screenwriters Roger Avary and Neil Gaiman have given this particular telling.
Advertised as the archetype of action movies, Beowulf is really more thoughtful than that. I'm afraid most viewers won't get past the gee-whiz effects and the way cool action scenes. But at its core, this Beowulf is about flawed humanity and overcoming obstacles that reside within.