Initial reaction, commenting strictly on the UI, I know nothing about the background of this project or how the books were acquired. It's a nice UI, and some of the classic works I expected were there. For example, I searched for Jonathan Swift and it quickly pulled up 8 works that pretty much cover everything he wrote. Reading and navigating is simple, texts were clear and well laid out. Like it.

A couple of basic suggestions for your UI:
* Your Search box flips to "Clear" when a user enters text in the search field. That is odd and an unexpected user experience, as user's only option to search is to press Enter. I'd leave the Search button as Search, let user clear their own text manually or clear it automatically after search results returned.
* Your Search results are not completely accurate. The string "Jonathan Swift" pulls up 8 volumes of poems and prose works, but excludes other works that you have by Swift, such as Gulliver's Travels. So that is worth checking out.
* Your page-turning arrows are overlapping the text when using a larger font. Might want to adjust margins a bit more or make those buttons more transparent. This appears to be an issue only when the TOC is open during reading.
* There are a few layout issues, not a big deal. For example in Shakespeare's complete works, you have all the text of the speakers lined up directly under the character's name. A better layout is like the Pelican print Shakespeare, and the Kindle William Shakespeare Complete Works by the Royal Shakespeare Company, ed. Jonathan Bate. These versions improve readability by indenting the speech under the character's name.