To understand some of the images and references in this movie, I suggest you watch the two previous Pokémon movies first: "The Rise of Darkrai" and "Giratina and the Sky Warrior". You will better understand where those other legendary Pokémon are coming from.
As a rule, Pokémon movies aim to touch the audience and make them sympathize with the cause presented in the film. While I could understand Arceus' anguish, that was about it on an emotional level. This movie just didn't do anything for me.
They assumed too much, not bothering to work for it. Team Rocket was just tossed around for a few brief comical moments. Our heroes did nothing overly spectacular. The new characters remained empty and uninteresting. I'm not sure if I liked Arceus' voice, either (although that isn't relevant to the story, right?).
I guess after making 11 movies prior to this one made them a bit lazy and they didn't bother making this as sharp and dazzling as some of the other movies are. A shame, because there was potential in this. It was very nice to see Dialga and Giratina again, though.
