I like the idea of a pre-chapter quiz, to help identify what I can skip and what I should concentrate on.

I also like the idea of integration with desktop apps where I could copy/paste code, link directly to the feature being discussed, etc.

I don't like audio/video features in ebooks, especially when the material isn't also covered in text. With text I can scan/skip over material I already know and spend more time on material I need to concentrate on - neither of these options are easy with videos. It's also easier to find my place later in text if I need to switch to some other activity for a while. Volume and screen size can be an issue to, especially with decreasing hearing/eyesight as I get older.