A quick way to know if you're a nerd: if your first reaction to hearing about the film Beowulf was "Neil Gaiman is doing a screenplay adaption of an Old English epic!" then you definitely fall into the nerd category. And for those of you who are like me and reacted that way will find the result worth it. This is the best film adaptation of Beowulf that I've seen even though that's damning with faint praise. But Beowulf has some real problems which no script could ever help.
For those of you who slept through your medieval literature classes the original epic is simple. Hrothgar's mead hall is getting attached every night by the monster Grendel so he sends out a call for heroes. Beowulf shows up and kills Grendel but his Grendel's mother is even nastier and wants revenge. Beowulf kills her and becomes king. Then it jumps ahead a few decades to a dragon attacking his land and Beowulf in his old age goes out to face the dragon.
Gaiman's script takes a point of view of showing us the real events that had been interpreted by the bards. It's similar to Eaters of the Dead (or The Thirteenth Warrior for those who have only seen the movie) in that sense though Gaiman obviously retains the fantastic elements. His deconstructionist view is that Grendel's mother is, essentially, a fertility goddess who offers a kind of immortality in exchange for seed. It's a concept that hits all the notes that Gaiman likes (if you're familiar with his work at all then you can probably guess where that story is going).
The real problems in Beowulf come from the visuals. There's nothing inherently wrong with CGI animation but the application here is particularly bad. Rather than distinctive character designs Robert Zemekis chose to make the characters look as much like the actors playing them as possible. Instead of wildly fantastic staging he chose "sets" that might as well have been sound stages (with the exception of a handful of better shots). In short, he made a live-action film using entirely CGI.
Unfortunately that plunges the viewers right into the heart of the uncanny valley, the paradox that as CGI attempts to look more real the more a human observer will notice that there's something wrong. Characters don't quite move right, lips don't quite form the right shapes, the skin doesn't have quite the right texture (this stands out in particular since the movie features the youngest looking old woman I've ever seen). Their attempts at realism are just distracting which is not a good thing.
Another problem is that the actors simply didn't do a very good job. Hollywood loves to cast big names for their animated movies but the skills for acting in a movie are different from acting alone behind a microphone (even with ADR they at least have the advantage of pulling from their on set experiences). Anthony Hopkins does the best work as Hrothgar, and Brendan Gleeson as Beowulf essentially gets to shout a lot and that's hard to do really badly. Angelina Jolie, on the other hand, acts like a drunk forty-year-old trying to seduce a teenager and I don't think that's quite what she was trying to do and John Malkovich was so sedate I was wondering if Valium was available in eighth century Denmark. I do have to compliment Crispin Glover as Grendel for learning his few lines in Old English.
It's a tough call for me but I think that the story outweighs the visual problems that the film has, but ask me on a day when I'm thinking about quality animation and I'm likely to go the other way. I'd say the breaking point is Neil Gaiman; if you're a fan then you'll be more inclined to overlook Beowulf's faults and find that gem in the middle but if you're not then you'll find yourself staring at the cold, dead manikins that Robert Zemekis is attempting to pass off as human beings and wondering why you went to see the movie.