I think that my favorite part about this book was probably the footnotes. The math was a little above my skill level, but John Green did a pretty good job of explaining it, and it definitely fit the character to be so math-oriented. I love this book, though there are definitely others that I prefer, even by John Green. My rating for this one is roughly a 3.5, though I felt it deserved to be rounded up. It really is a good book. My favorite character was Hassan. :)