This is some good art right here. It has a lot of detail. It is really imaginative. The style is simple yet interesting and pleasing to the eye. I can't think of any feedback that would improve this as an overall work of art. However, since you're looking for criticism, I'll share my thoughts on how I think this could be a better children's coloring book cover. First, I think that there is just too much happening in this image. All the little things you put in can get distracting. I think a coloring book cover should be more simple; less stuff to look at. A heavily detailed picture like this would be better cover for a book like I-spy or something. The second thing is that you should probably have the title around the centre of the page instead of at the bottom right. I hope you find my thoughts useful and satisfying.