Humans by Matt Haig

When an extraterrestrial arrives on Earth, his first impressions of humans are less than positive. Taking the form of Professor Andrew Martin at Cambridge University, the visitor is eager to complete his task and hurry back to his own utopian planet. Disgusted by the way humans look, what they eat, their capacity for murder and war, he is equally baffled by the concepts of love and family. But as time goes on, he starts to reconsider.