The backstory on how he saved the world also made me "meh" (He creates the entire universe but can't take on a huge asteroid, which is part of his creation, without dying? Gets defeated by hundreds of slave Pokemon? Yeah, I guess "God" isn't so tough).
Also, the way they made Arceus too talkative and emotional/sensitive repulsed me a bit.
Now, I don't know about you guys, but when I've first heard about the existence of Arceus, I had to check him out. Tried to Action Replay cheat to unlock the event and damn it is amazing. It had such an effect on me using the Azure Flute (Oh damn! The theme!) and climbing those golden stares to capture the legendary Arceus.
Arceus had such mysteries surrounding him it made me go gaga on wanting to know more. And the less you knew about him, the cooler he was. I think it would have been better if they made him mute or less talkative (if he wore to talk, it should have been in a monotone voice).
Strangely however, I thought the voice actor who did Arceus did a good and bad job all at the same time.
The thing they did Arceus in the game were very fitting, the very vague side story you could read on Diamond and Pearl (which can be found here if you didn't read it :
http://www.youtube.com/watch?v=uKW4N8-5JNU, the themes :
(
http://www.youtube.com/watch?v=4_h9Tu2Qd-8,
http://www.youtube.com/watch?v=Z3xZa9hY3qg&feature=video_response,
http://www.youtube.com/watch?v=MtSN_rcYM44) and the overall atmosphere. It's disappointing that they didn't include much from the game onto the movie.
However, I can see why they choose to go with the way they went, there wouldn't be much of a fight if Arceus wasn't angry.