Well I loved it and here's why with LOTS OF SPOILERS.

Rating: 8/10 (15 November 2007)

From the outset, Beowulf is bawdy, bloody, and beautifully constructed. Neil Gaiman & Roger Avary's screenplay is impressively faithful to the original saga in general; the departures add colour and depth to the world in which the characters move, and help to make a point about the innate hubris of any alpha male.
Gaiman lives up to his reputation for having "a dirty mouth in at least seven centuries", and I look forward to one or two long-lost expressions returning to the nation's playgrounds when this goes on general release on Monday. While the BBFC may consider the language mild enough and the gore artificial enough given the fantastical setting, do not go into this expecting the kids' version. When Grendel attacks, not only do you get mystical blue flame, but you also get arterial spray. We see shadowplay of the monster ripping a man in half and think "copout" but then his torso, complete with exquisitely rendered dripping entrails, is thrown into the shot as he expires. A warrior's head is bitten off and Grendel chews it, lazily, like a gobstopper, for at least a minute. Fantastic.
The CGI itself is for the most part excellent. The gamble has paid off, since the subtle wrongness which affects CGI monsters and items in live-action permeates the whole film, enabling suspension of disbelief. The one sticking point is Angelina Jolie; allegedly deliberately overairbrushed (even more so than the other women featured) to lend her an ethereal quality as Grendel's hot momma, she often looks more like she's acting in a cut scene from Tomb Raider:Norse. In her defence, the prehensile, Gigeresque hairdo and the seamless spike-heeled feet are cracking ideas, reasonably well-realized.
Ray Winstone struggles manfully to hold in his Laaahndahn tones and mostly succeeds. Brendan Gleeson is excellent as his dignified lieutenant Wiglaf. The ladies are suitably decorative with just enough pinches of sassy dialogue, dignified in the delivery, to remind one this isn't actually so Boy's Own as all that. Malkovich walks the fine line between oily and sparky as ambiguous Unferth, and Hopkins is enchantingly barmy as ageing Hrothgar, calling to mind his sterling Van Helsing in parts. The slight accent slips that all the main characters suffer actually works in their favour - like the American and Scottish accents in Dangerous Liaisons, they help to distinguish the peoples - The Geats occasionally sound English, The Danes oddly Mid-Atlantic Welsh (Hopkins and Malkovich must have talked at each other for hours to nail that one), giving the impression of different peoples using a lingua franca. In a touch which made me bounce up and down in my seat a bit, Grendel speaks Very Old English. In fact in the scenes taken directly from the original text, he delivers his lines verbatim. The additional scenes inserted, apparently to give the monster a bit of motivation and set up the horrible truth of Hrothgar's shame for the uninitiated, are well-written (as you would expect - this is Gaiman after all) and actually manage to imbue Grendel with a bit of sympathy - this is definitely a product of a culture which no longer thinks in black-and-white terms.
On that note, another deviation from the original text is the position of faith in the film. At the start, all the main characters with the exception of Unferth are firmly pagan. Many years later, when Beowulf faces his third demon-battle, Christianity has moved in and Unferth is now a priest. And that's it. No debate, no manifesto, no bending of the story to serve a certain religious viewpoint (unlike the original).
Almost.
If you forget the dragon's first attack.
The scene, which ends in a horribly injured Unferth being carried to safety on a smouldering cross, bleeding onto a white snowfield, screaming "The Sins Of The Fathers..." appears to carry more than a few references to album covers of a certain nature. The fact that the first building the dragon sets fire to and stomps on is a church makes one wonder if Gaiman had a certain element among the viewers in his mind when planning it.
So anyway. To summarise. Emotional bits (Hrothgar's plummet, burials, aftermaths of attacks, any scene with ladies in): reasonably moving except for the singing. Who let Glenn Ballard in? Acting: some scenery-chewing but that's mostly due to the bombast of the script. Script: An excellent adaptation overall. Effects/Animation: Pisses all over Polar Express, and indeed Final Fantasy, from a great height, and the dragon is *gorgeous*. Keep an eye out for: some genuine, extant Viking artefacts in the prop basket, visual gags involving men staring at boobs, excellently rendered hideously graphic violence, some comedy cock-obscuring, Ray Winstone's little homage to Malcolm McDowell's Gangster Number One, and one of the most stupidly heroic and gruesome moments ever.
Heartily Recommended.