"Against Empathy" by Paul Bloom is a book on empathy. The author is not really against empathy but he's trying to understand (or explain to us) what does the definition of empathy mean and look at the advantages and disadvantages of empathy (giving to someone equals not giving to someone else, fighting someone means empathizing with someone else).
The author is encouraging us to critically look at the empathy. He nudges us to discover our own biases and view critically ourselves when we try to empathize.
The book is written in a style of a classic psychological-sociological work (similar to the ones you get to read in college). It is lengthy and philosophical. What did I learn from this book? I learned that psychologists can literally take one emotion, name it and write the whole book on it and I admire them for that. Did I "agree" with everything written? No. There were some things said that I didn't agree with (not at all related to empathy by the way), but it was an interesting experience.