I found a very interesting review in the December 2008 issue of "The Page," a local SCA calendar of events. Unlike most movie reviews found online or in newspapers or magazines, this was an actual analysis of the stuff I had been trying to figure out about the movie all along: what was the point of it all? For the sake of fairness, I will mention his ideas to give a more complete picture of what may have been happening in the movie.
David Orphal brought up a very thought-provoking idea: Beowulf's director may have been trying to blend both Beowulf and Arthurian legend. In the 2007 movie, Hrothgar stands in for Uther, and Beowulf as Arthur. Quite a lot of it fits. This is the closest thing I've yet heard to explain the ridiculous sexuality of Grendel's mother, though it's easy to see why the director's vision of melding two distinctly different legends is difficult to interpret, as far as I'm concerned, considering you have to make the leap to visualize Jolie as both Igraine and Morganna (and perhaps Eve, while we're at it). At the very least, this helps explain why Beowulf becomes Hrothgar's heir, rather than (as in the poem) returning to his own country to rule.
The analyst writing the review had an additional thought as to why Beowulf was such a flawed character: his flaws, it is hypothesized, make his sacrifice at the end even greater. He becomes a hero, instead of being a hero all along.
Whatever. I still think the movie sucked.