Oh Arceus, this movie was bad. This has mostly to do with Arceus as a character itself. First off, the voice... the voice!! It's so... bad. I'd rather have him not have a voice at all. Then the writing of its dialogue, with repeating the same line like three times over in the movie, it using "take this" and "alright". Really, come on? We're dealing with a supposedly godlike creature here.
Secondly, the legends say it is supposed to have created the world and the dimensions of time, space and reverse. Yet it has to offer a part of its very own life force to recover a patch of land. Urgh... how's that work?
Third, the supposedly godlike creature, with enough intelligence to use human speech, yet is so blinded by rage that it feels the need to destroy life on the entire planet for the betrayal by one man. No... just no.
Fourth, lol at GOD having its memory re-written at the end of the movie. Lol.
More lol for everyone in the past calling Pokémon 'magical creatures'. I mean, Pokémon are a normal thing in that world, why aren't they just called animals or something. Although this could maybe be an issue with the translating, I don't know what the original Japanese script uses.
That scene in the beginning when Pikachu and Piplup almost get sucked into another dimension and then get saved by Dialga. Ash going "cool" instead of freaking out over the entire lake turning into a water tornado and the sky transforming into a black hole, with the rest of his friends just smiling beside him. Yeah, totally natural reaction there. Also funny how they don't even bother trying to run from the 2nd time it happens, minutes after the first time. They just stand there.
The only thing I liked about this movie was the evil guy with the red hair (did he even have a name?)