1. Have a background image that looks like paper. No, a solid white or tan background doesn't look like paper. Paper has imperfections in it, dirt, a grain, and you can faintly see the other side of the page. Except for the latter, this is easy to achieve. Simply scan a bunch of blank pages, and use the scan for backgrounds!
2. No, having a background with a fake coffee stain ring doesn't work, because it's the same on every page. You need a few dozen pages, each with a different stain.
3. A printed page is imperfect. The letters can be uneven and blotchy. No, don't have a blotchy font. Have maybe 20 slightly different versions of the same font, and randomly select a glyph from one of them.
4. Books open to two pages. Not one. Two. The ereader should show two pages side by side, like a book.
5. Book fonts tend to look better than ereader fonts, though I cannot explain why.
But most of all, the sterile perfection of the ereader is like a drummer who is too perfect. Introduce error in it, it makes the music easier on the ears, and the books more pleasant to read.