Another great John Green novel. He has a way with words and characters as well as symbolism that I can't even describe well.
The plot is about a 17 year old kid named Colin. He's an ex child prodigy who wants to matter in life and wishes to become a genius. He's also dated 19 girls named Katherine (hence the title). Colin's journey is amazing to read, watching him grow up and realize some ugly things about himself. The supporting characters are fantastic too. Like Hassan. He's hilarious, but he also goes on a meaningful journey as well. All of the main characters do. It's wonderful to watch how they deal with each situation in their lives and how they come out of it. All in all another wonderful work from Green, can't wait for his next book. DFTBA! :)
EDIT: I just re-read this, and honestly, I don't remember why I liked it so much. It just didn't do it for me this time around. I still love John and his other novels, sadly not this one.