I see a lot of "almost" bookshelves. They hold books and look "design-y" but they waste energy and space. If you are really into books, it's not about the cute shelves. It's about the books. Make that space hold as many as it can.
Floating bookshelves, these are bookshelves I like. Looks like you could do this with an IKEA kitchen wall cabinet minus door and turned horizontal to mount. IDEA for narrow wall next to our kitchen wall