It's an animated kids fantasy about a scientist who thinks that there's lots of little people running the forest and everyone thinks he's nuts, including his daughter, but it turns out he's right, and she gets shrunk and into a battle between good and evil. The premise is kinda silly, the emotional stuff falls a bit flat, but it's rather gorgeous looking, the action sequences are well done, has a decent plot and a few laughs. I particularly liked the bad guy voiced by Christoph Waltz who reminded me of the Kurgan from Highlander.
If you've got kids, worth £3.50 of your money to hire it.
* Other video rental services apply, I'm not getting a kickback for this