I believe that the poem is a better definition of a true epic. In the poem, Beowulf does more heroic like things, when he rips Grendels arm off with his bare hands, with only using his pure strength, but in the movie Beowulf wraps a chain around Grendels arm, and uses the door of the Mead Hall to repeatedly smash his arm in the door until he rips the arm off completely. In the poem, Beowulf always tries to make himself better known, he goes back to his kingdom to tell all of the Geats of his accomplishments, and whenever he dies Beowulf asks his warrior to build him a tower with his treasures and his best warrior becomes king.
A difference in the poem and the movie is that Beowulf stays and rules the kingdom that he saves,