This is the 12th movie in the Pokemon series, with movies 7, 8, and 9 yet to receive a UK DVD release. I have the American version, so can review this one too, as I am sure it is not very different.
This movie tells the story of Arceus, a powerful Pokemon that was betrayed in the past and vows to seek revenge on the human race once awakened. Ash, Dawn and Brock arrive at Michina Town, just before Arceus awakens when they are reunited with Palkia, Dialga and Giratina from the 10th and 11th movies. This leads to Arceus attacking the town, battling the three legendary Pokemon and Ash and friends traveling through time to resolve Arceus's anger.
This movie isnt the best one in the series, there is a lot more dialogue then action going on in the movie, and suddenly Palkia and Dialga were no longer angry with each other, which was resolved as well as I hoped. Another Pokemon, Heatran, makes a minor role, similar to Regigigas in the previous film, but slightly more. I was hoping for a big battle between the four main Legendary Pokemon, but was disappointed mostly. There are some good moments, but they are far and in-between, and the animation was pretty nice as well.
If you are a Pokemon fan, it's worth a look at least. Just don't give your expectations up too much