What does the owl-eyed man find extraordinary about the books in Gatsby's library?

The books are real books, not just the front cover for show.

However, back in 1920's when a book was binded the pages were still stuck together, so when somebody has read the book they would have to tear the pages apart (therefore leaving jagged edges)

The owl-eyed man notices that the books have not been read at all, this is the irony in the books, they are as good for show only.