There are many long detailed reviews of Purity on the Internet that discusses the themes, plot and writing of this book in great length. Rather than add to their numbers, I give you this.
Based on reading Purity, here is a list of things that Jonathan Franzen likes:
* writing about penises
* writing about masturbation
* the sound of his own voice
* feeling like he is cleverer than everyone else
* going on and on about the things he does not like
Based on reading Purity, here is a list of things that Jonathan Franzen does not like:
* kids today
* the Internet
* modern life
* attempts to address environmental issues
Apparently Jonathan Franzen is married, which surprises me because this book reads like it was written by someone who had never actually spoken to a woman and is attempting to reconstruct them based on what he had read in other books.
Purity is not good. I strongly advise you to read the Intercept review Stop Sending Me Jonathan Franzen Novels instead of the actual novel - it's eminently more satisfying.