I felt bad for John, having to endure that leg wound for the rest of his life, on top of his recurrent nightmares. I could understand how he would come to define himself by that wound, reach ever higher levels of despair. And Rex was just as pitiful, having to live on the streets as a dog in order to get by. They were each other's salvation.
I enjoyed the funny moments sprinkled in the book (when John was talking to the dog (like any other owner, except us readers knew it was actually a man) or the first time Rex turned into a man.
There wasn't much development for the characters, their history and interactions but it was nice, even in its simple form. Coupled with nice writing style, this is worth reading.