I actually watched the movie before reading the poem. Did anyone get the idea that Grendal was King Hrothgar's son? I was surprised when I read the piece, because I had the idea that King Hrothgar had succumb to temptation and slept with Grendal's mother and therefore was the father of Grendal. This is why Hrothgar could not kill Grendal, he could not bring himself to kill his own son. There was a scene when Hrothgar had the opportunity to kill him but did not.
Also Hrothgar's wife would not sleep with him, because he had touched "her". I took this to mean Grendal's mother. When Beowolf killed Grendal, Hrothgar seemed to be relieved on many levels. It was as if someone had cleaned up his mess and his contious had been cleared.
Later it was implied that Beowolf slept with Grendal's mother to give her a child to replace the one that he had killed. I got the impression that Beowolf succame to temptation in the same way that Hrothgar had, therefore coming full circle. Now there was a Dragon, hence Beowolf's son.
I have never seen a movie ADD themes that did not appear in the story. I actually thought the themes in the movie were better. I will have to go back and reread Beowolf and compare the two.