The main features I'd love, which some other people have already mentioned:
1) A progress bar at the bottom, showing me how far along in the book I am. For many books, this is unavailable. It's a daunting task to read a large book, such as War and Peace, without knowing how far along you are.
2) A go-to-page feature. If I want to skip to page 300, I shouldn't have to hit "next page" 300 times.
3) An easy way to remove books out of my "Currently Reading" section. I have no idea how to remove them right now.