Lest We Remember

Some people were disturbed enough at the fact that Grendel's mother lives in the end to write off the movie as a poor adaptation.  Yes, in the original poem Beowulf is a hero mostly because he kills Grendel and his mother; but in this adaptation, Gaiman successfully grasps onto important themes of Beowulf's personal story, and uses Beowulf's failure to kill Grendel's mother as a device by which he can make his adapted theme clearer; I imagine that this is the best way to make a reasonably good movie out of a poem so epic in length.

In the movie, Beowulf lives his life out as a hero, never quite feeling like one; all of his subjects believe he has killed both Grendel and his demon mother; he is living a lie.  The melancholic undertone was engaging cinematically, and it lent credence to his failure to kill Grendel's mother.  His final battle with the dragon is charged with obvious parallels between Beowulf in his old age, and Grendel in their battle decades ago; Beowulf is chained to the dragon as Grendel was chained to him, and Beowulf finds he needs to slice his own arm off in order to tear out the dragon's heart, just as Grendel's arm was rent during his battle with Beowulf.

In the end, the non-heroic main theme was evident: we are all the same, all one.  We live and die with our own pain, our own failures, and our own hopes and dreams.  Beowulf is the monster he killed, and a monster still remains ... he kills the monster of the day, but "his demon" lives on; I thought it was incredibly well done.