Great job! But I have to agree the back ground is a bit under done, but honestly I really can't say anything because my back grounds suck >< Still you've done a WONDERFUL job! What kind of poster is this for? An event or something? o.O
I really like this piece, and the retro-ness oozes out. The only thing that i would like further would be maybe some subtle shadows on the person, but that might take away from the line and color aspect of a retro piece.