I really liked this book, especially the slow unraveling of Myself's mystery and the descriptions of the House, but I think I was led astray by all of the positive reviews. 

Because, while Piranesi is a good book with an interesting format and mystery, I have read similar books that are similar in subject that hit a little harder and push the boundaries a little further. (A personal favourite is Beneath the world, a sea.) So ultimately I was a bit disappointed by the end.