I read this book just a couple of weeks ago and it is still engraved in my head, it was such a fun book to read! Though I had to also agree with other people that the first few pages were kind of boring. But don't worry much! The book gets even better when Colin and Hassan meet Lindsey!
But let me just clarify something to you before I further indulge myself in this review, this book contains lots of swearing and has a few scenes that are not safe for children! I honestly don't mind the swearing on every few pages because it shows that John Greens' characters are quite honest and raw, this book is supposed to be for Young Adults (Teens) so there's no big deal.
The book starts quite boring, but as soon as you reach the part where Colin and Hassan meet Lindsey, you'll find it much more fun to read their adventures and stories. There are also some flashbacks on Colin's past with the Katherines he had been with (but these flashbacks are mostly about him and Katherine I). Colin likes girls whose names start with Katherine, which is why he has made a theorem about Dumpers and Dumpees(which I will further talk about later in this review)
And as you have seen with the other reviews here that the book does contain mathematics and graphs but fear not! Colin will do most of the maths and graphing and he further explains how they work, John Green has even put several footnotes and also helps in explaining. The maths and graphing are just all there to help further explain Colin's -Theorem of Underlying Katherine Predictability- theorem.
Overall, this book is so fun to read since it is very humorous and is very relatable. It even shows a lot about predicting the future and how smart people are not always right. I have found the characters funny and relatable, especially the supporting characters, Hassan and Lindsey. Who has always made me laugh whenever they talk. Of course, this book isn't for everyone and not all people can fully appreciate it but I hope my review helped you understand it a bit more! Kudos to John Green for writing such a fun and beautiful book!