First off I have to say that I'm not the best artist by any means, so my opinion is just that, my opinion. But since you asked...
Overall I think you've done a good job. There are some things to work on. Your linework needs some discipline, I think. If it's supposed to look like a sketch, leave in the guidelines and keep it sketchy. If it's supposed to look like linework, ink those suckers or clean up the curves. There are a few things you can do when scanning in Photoshop that will clean the lines up for you. Check out Polykarbon's website for a quick overview. I always say that doing it the manual way first is better though, gives you a certain perspective when you have the shortcuts. There's really no easy way to just do it, practice is the only means to the end. Always practice.
One more thing, aspiring to somebody elses style is a great way to get started, and to learn new techniques and ideas. I myself am studying a lot of Yoji Shinkawa's stuff now. Ideally though, you want to be able to do you're own work. Don't pigeonhole yourself as a guy who draws Ryoko exactly as the original. That's great as a start, but don't let that be your barrier. Learn how to assemble Ryoko visually out of basic shapes: like an architect builds a structure, start simple and flesh it out. Ideally with some practice, you won't need that reference picture. And beyond that, you can create something that has no reference at all, that is to say: unique.