The top look is interesting because of the large space above the rows of books. Generally, bookcases are designed like the one on the bottom, with the shelf size just a little higher than the books themselves. But assuming you have the ceilings and the space, the top look — allowing double the height of the books — looks really clean and almost like installation art. (Plus, the bottom picture has the bookcase in the bathroom, which I don't really support.) In both cases: fat shelves.
top from Christoph Theurer, bottom from Catherine Ledner