I agree, it's much too dark, your shadows overwhelm the entire composition. I downloaded the image, used the dodge tool to lighten it up, and I found many coloring mistakes such as messy coloring and bad shading. I think you could seriously improve this, first by lightening it up (you know, just a suggestion) and fixing the aforementioned mistakes.
Good try, and you have my respect for the effort you put into this, but it is a little bit to dark. I like a lot of your other colorings though, so don't worry.