I love this!! You can definitely tell how much care you put into this with the detail -- it's so rich and the characters are so full of life! I love their expressions and how you differentiated each of them from one another. The color scheme is very nice, too, and fits with the overall theme of the piece well.
If there's anything that I would say, though, that could be improved, it would be the characters in the background seem to be a bit too much "in focus," if that makes any sense? I think that if they were a bit more faded -- similar to how you did the blimps -- it might meld a little better.