I read Paper Towns because I had read another one of John Green's books, The Fault in Our Stars, which was a very moving story, and I saw that the Paper Towns movie was going to be released (and you always need to read the book before you see the movie!). While the main character in The Fault in Our Stars is female, I did not take any issues with her portrayal by a male author; interestingly, I did have some issues with the male main character's view and portrayal of the love interest, Margo, in Paper Towns. I think part of this has to do with the underlying philosophical discussion that is the crux of Quentin's (Q for short) coming of age story. Margo leaves behind a copy of Walt Whitman's Leaves of Grass for Q as a clue for him to find her. He reads the book many times, each time realizing that who he thinks Margo is is only his perception of her based on a performance. She seems to have a character she built that those at school or people she socializes with see; as Q starts to realize, there is a whole other Margo that lives internally and when she is alone. Subsequently, because of this dissonance between the Margo performer and the internal Margo that Q starts to realize, the difference becomes jarring between how Q describes and thinks of her, and the Margo we come to meet in the end of the book in Agloe, NY.
I think this dissonance is done on purpose. As Q reads in Leaves of Grass, he begins to think about how we are all connected, but also maybe it isn't possible to know someone else entirely--to know their true self. And so the dissonance would make sense as Q starts to remove the layers of the facade that Margo has built for the outside world. And in fact as Q realizes, he really knew very little about Margo, and everything he knows about her is truly superficial--her looks and the act her performs. He is even surprised when he compares the Margo he knows to the Margo others knew and finds that those are different Margo's. He starts to see a little of this unraveling the night of their Great Adventure, but by the time we see Margo again at the end of the book, she seems almost like a different person. I think that is partly because in the intervening time, he has started to realize that he didn't really know Margo, and his image of her starts to break down.
I think overall the philosophical story is very nice, but that because Margo never seems like a real person (even in the end because she is so disjointed from previous views of her, I found it difficult to find her a believable character), this story may be better suited for tween/teen boys who might be going through their own coming of age story.