This book is told completely through e-mail exchanges between who we are told is a psychiatrist (who uses multiple e-mail addresses), a person who claims to be a former patient, and then third person who is only tangentially involved.

It is a bit hard to talk about this one while being mindful of spoilers, especially since it was so short. 

The book does do a good job in having readers relate to the psychiatrist, even though the patient contributes just as much to the conversation. I was a bit confused at why the psychiatrist would feel the need to use several throwaway e-mail addresses for a portion of the exchanges. It is somewhat explained, but I'm not sure if the explanation explains the quantity and frequency of the changes. 

I think the book also succeeded in keeping the story fast-paced and adding more elements as it went along to get the reader to increasingly question the reality of the situation. The patient does offer an explanation as to why he started these conversations in the first place, but an alternate explanation is also given towards the end, so I suppose it is up to readers which one they will choose to believe. There is definitely a feeling of uncertainty and a growing sense of tension/unease as it progresses. The ending felt pretty open-ended, and I think either explanation could make sense, although I do have a preference as to which I would like it to be.