Everything looks not bad. Graphics are interesting, small dog is real cute :)
Music a bit to calm and depressed for such game as for me.
When small dog on the big dog back it can't jump up + forward. He just fly in space and It looks weird.
In bay 04 when both dogs are in the right side bigger dog can't jump out.
I think you need to work with collision boxes for both dogs. They are buggy.
Level design isn't perfect also.
Good luck.