How can you adapt 3 books spanning about 750 pages of epic fantasy into a single 90 minute movie?
If Legend of the Guardians is any indication, you can't.
In cramming as much of the books into this film as possible, little is setup well enough for you understand what's going on, and if you do understand what's going on, you won't be given the context to care.
Another problem is that a lot of what they're bringing in from the books just isn't conducive to film. Many of the names (ex. Ezylryb, Otulissa) are hard to hear and remember when they're just spoken. And so much of what these owls do throughout the film has to do with how the feel in their gizzard, which in this rushed pace and without the descriptive power of prose is just confusing.
The fact that this is directed by 300 director Zach Snyder is evident because he obviously has a patent on obnoxious and pointless slo-mo. The idea of the 3D fad turning movies into cut-rate theme park rides is only buoyed by film like this.
A major part of artmaking is composition; selecting and enhancing certain aspects while minimizing or eliminating others in order make what you want to say more clear. On the other hand the hyper-realistic style of Legend of the Guardians does themselves a lot of harm by piling on detail for its own sake while covering up parts that make things interesting, or at least understandable.
There are also many times when you can't tell two characters apart from one another, which is compounded even further when they're in a swooshing, fast-cut action scene.
I will give the production studio Animal Logic credit, Legend of the Guardians is far better than their previous film, Happy Feet. Being goofy and cartoony isn't well suited for this hyper-real style and that's restrained compared to Happy Feet, but when it does happen it still drags on the film. Also not hammering us with "celebrity voices" is an improvement. There are a few well-known actors in this such as Helen Mirren and Geoffrey Rush, but they don't stick out like sore thumb like Robin Williams assaulting your ears in not one, but two characters in Happy Feet.