It looks good enough, especially for a quick doodle. Why not set off some time, sketch it properly, and spend an hour? If you did, it would look way better allready, and it's only an hour of your life!
Personally, I'm old-school-ish when it comes to art programs, and imo they should only be used to clean up an image, contrasts and such. If one relies too much on digital reproduction, the image will look digitally made.
That's not bad in itself, but in order for a digitally made image to look good, it has to be *really* good. The worst thing I know is cheap and fast "dust clouds" or "shinyness effects" added digitally, that just stand out like sore thumbs against the rest of a clearly hand-drawn image.
Or "real looking brush strokes" o_-
/digression