Personally, I want the following in an ereader.
1. E-ink .... color one day.
2. Screensaver, that is the current or last book read, cover.
3. Decent impact proof cover, with transparent front.
4. Built-in evenly dispersed light.
5. Waterproof, sand proof, etc.
6. Glare proof.
7. Long battery life.
8. Decent storage, supplemented by USB thumbstick.
9. Folders of course, with a use author name option and collections.
10. Folders should be re-nameable and ebook shortcut can appear in any folder.
As for ebooks themselves, they should all come with a summary/blurb. So that they can be read anytime.
11. Summary popup dialog while reading ... you don't leave current page.
12. Shown as screensaver instantly by a button click ... device remains off.
13. Ability to Wifi etc to same brand ereader, if just to update last page read.
And no doubt some more things.
P.S. Font types & sizes etc and background colors/shading/brightness goes without saying. As does bookmarks, notes, highlights, etc.