I recently finished an e-book and the ending took me by surprise - not because of the content but because I wasn't expecting the book to end so soon.
This cannot happen with a physical book, and it seems to me authors intending to publish an e-book should give this some thought. A contents list at the beginning would help, as would using chapters. The e-book which took me by surprise was written in a series of sections, some of them quite short, but without chapters.