Cheery, huh? I guess that may be one of the reasons Gaiman and Avary chose to end the film in the middle of a choice. They were right in attempting to show the hollowness of "heroism" (although the hero's own demise is undeniably "heroic" and the result is more cautionary tale than lament). In the original, the battles with the three monsters only take up about one-third of the poem, making it more of an elegy than an epic.
And upon the hill-top the warriors awokeThe people's agony before Beowulf's pyre blends with the roar of the blaze until it becomes one keening force that quiets nature ("the winds") with its power. The grief and the fire become indistinguishable from each other, blurring the boundaries of physical fact and spiritual need to the point that it is unclear whether the disintegration of Beowulf’s body is the direct result of the flames, or the effect of his people’s agonized wailing, "hot unto his heart." It isn't just the loss of their hero that they're mourning, but the end of their way of life, the senselessness of war, and the void left by their gods. (I found it quite telling that the screenwriters decided to throw in Christ with the rest of them--he is notably absent from the original.)
The mightiest of bale-fires. Rose the wood-smoke,
Swart above the blazing. And the roar of flame
Blended was with wailing, as still the winds became,
Till, hot unto his heart, it broke the Geat’s bone-frame.
Unglad of mood, in grief they mourned their great Chief dead.
And his Wife, with hair bound, her song of sorrow said,
Over and over: how ‘t was hers to dread
Days of harm and hardship, warriors’ fall and grame,
The terror of the raider, captivity and shame.
The sky the reek had swallowed.
I was lucky enough to hear Seamus Heaney speak while I was in college. His phrase, "Poetry is a plow that turns time up and over" brilliantly applies to the necessity of works such as Beowulf. He said that through poetry we are able to more fully comprehend the sorrow of an ancient people facing unconscionable tragedy. Contemporary news via the media slips past us much too easily to be absorbed. The agony of nations is effortlessly offered on the silver platter of the 30-second sound bite. Because worldwide suffering dwarfs modern society’s ability to assimilate it, we need art and poetry to help us keep hold of our humanity.