Really like the pieces individually, but the lighting in your composite scene is too dark to really make out any detail, and a lot of that hard-work that obviously went into the pieces is lost.
I agree that the lighting is a bit lacking. You need some ambient light in there. Also the lighting is pretty flat and there doesn't seem to be any natural lighting at all (in this case the moon!) There's barely any shadow showing up in the composite, making the character and motorcycle look sort of pasted in. Maybe having…