As the title of the post says, no good story survives contact with Hollywood screenwriters, and Beowulf is no exception. Honestly, if I hadn't actually read Beowulf, I wouldn't have had nearly as much trouble enjoying this movie: it's a decent story on its own. Alas, it's got just enough plot and characterization from the epic poem for you to know how badly it's been mangled.
It's not nearly as bad as the Christopher Lambert Beowulf, mind you. That was a tragedy of unprecedented proportions. On the other hand, it doesn't treat the source material any better than Beowulf and Grendel did. There's also a style to it that's very reminiscent of 300, which I suppose is a good thing if you liked 300. In any case, it certainly hasn't knocked The 13th Warrior out of its place as the best screen adaptation of Beowulf ever.
If you try not to compare it to the poem too much, you can probably enjoy it as a run-of-the-mill popcorn flick. It's got plenty of well-paced action, and there is a moral to the story. It might do with a bit less random shouting (one of those things that reminds you of 300), but that's endearing in a way, since it gives you something to heckle. This is a movie that begs for some good-natured heckling. Any movie that forces you to look at a fat and mostly naked CGI version of Anthony Hopkins needs to be heckled; to do otherwise invites madness. (If Shepherd Book is to be believed, I'm going to the special Hell.)
To my credit, I had the foresight to smuggle a couple of mini-bottles into the theatre to spike our soda. I only used one, and frankly, I should have used both for this movie. I'll be happy to watch this movie on DVD when it comes out, but I never intend to watch it sober again.
The final battle kicks some serious ass, though. No matter how badly the story offends your literary sensibilities, stay for that last round of eye candy.
Update: SurlySeraph on the Giant in the Playground forums had this to say...
"I feel like I just saw the hellish offspring of 300 and Troy."