This might be just me, but I don' t see the cohesion between the styles of art, animation, sound and story. And it's not that they necessarily don't go together, but these elements - they just seem slapped together to me. I do enjoy them separately, but the way they are blended, I feel, could be improved.
I'm judging this movie on it's own merit, as I haven't seen any of your previous entries, but I presume the characters were introduced before, since they have some chemistry going on and seem to know each other. Though in the movie itself there is very little explanation given.