Great song in the opening. Where did you get that? However, I feel like opening is too long and I thought it was the main toon for quite a while. The random violence is kind of dumb, both in the opening and the main toon.
The sped-up voice is difficult to understand, and at first I thought they were just soundclips from one of the many violent-cute-animal cartoons out there. Perhaps the voice could be more normal... or perhaps the characters could just speak gibberish. The story is simple enough that their tones of voice would be all that people need to understand them.
I like the colours. All of them. They contrast tastefully. Though I feel like the art style is too simple yet, it shouldn't become too complicated if you want to keep those great colour contrasts.