The sky is great, but the tree looks like you spray canned it.
And I think it's supposed to be happy.
It's ambiguous, to me at least, whether the protruberances on the upper body are breasts or arms. If they're breasts, I think squirrels have about six.
Have you thought about entering a version of this for the pokemon challenge? It's got that cutesy round thing going on, like pokemon.
The sky is quite nice. Did you borrow the design or just the colors?
The greenery needs more details imo. Other than that I think this is a nice first piece.