I think your illustrations don't require any criticism at this point. They just speak to the reader and tell the story in an engaging way. I also liked your color palette. It is consistent (which is very important), carefully chosen and the colors just complement each other.
I have to disagree with your feedback.The color palette seems okay but it's no where consistent -and it shouldn't be.
The banner is probably the best piece of design. As this is a long article, the images with too much whitespace slowly become invisible. The article is long, detailed and for must of us can get boring. The images should be preventing that. With too many light colors, huge whitespaces and extremely similar images I think it can get dull.
Hope my criticism helps the OP :) I should also mention that I like your style and the way you communicate. It's just that it could be better.