I don't know why so many of you hated it so much.
In the time the story was written/ transcribed there really was very little character development used in stories. And if you think about it, Beowulf was probably one of the first "action heroes", so it makes sense that it was an action film. And the cheesey dialogue about violating virgins and all that... that was par for the course back then.
They HAD to change things from the original. If they did a 100% faithful adaptation, it would be a VERY boring film.
Grendel a zombie? I don't know where you're getting that. For me, he was nigh on terrifying. That scream... and the pulsating eardrum... drool... and all the carnage at the begining. From what I remember, there never really was a good description of what Grendel looked like, so they just took liberties.
I love how you saw Grendel's mother as a monster only in reflections... it gave her a lot more mystery and made her creepier.
*spoiler*
I also love how they linked the parts with grendel and his mother to the dragon. And the whole thing where Hrothgar was Grendel's father and Beowulf was the dragon's... a brilliant choice (I would like to think Neil thought that up, but probably not).
*end spoiler*
the 3D was cool at first, but I sort of forgot it was there after a while. Oh, and the Coraline teaser trailer? It teased me TOO much... if you don't know what it is, you really don't get any idea from the trailer. But I can't wait to see it.