My Big 2:
1) Why page turn?, why not page down? English reads top to bottom. Seems like a big improvement would be a page down instead of a page across.
2) If I zoom into text I don't want to have to horizontally scroll, that's even more annoying that small text.
1)
Perhaps is because of what we are used to, but I read much better with page turn than with page down.
I read a book in the computer, and I read it scrolling down. It didn't feel fulfilling. It was like reading a web-page.
But having read a couple of books in my phone (with the kindle app) it felt natural again, I enjoyed much more the books that way.
And no, the quality of the book was not the question. It was a free download (by the publisher) and a year or so later I've bought it on paper and read it again. It was much more fulfilling this way.
Perhaps in half a generation or so people will feel more natural going down than sideways, right now I prefer the later.
2) If I zoom into text I don't want to have to horizontally scroll, that's even more annoying that small text.