Here is a few of mine:
1. No DRM
2. ePub format
3. Download to PC
4. Download directly to device if I choose
5. Synchronized meta data - if I rate a book, I want my rating to be visible to me on my PC, ebook reader and android smart phone
6. Night vision option on the Android app - choice of night colours
7. Offer some free ebooks - perhaps #1 in a series. If I like it, I will buy more in the series.