I'd say my rating is really closer to 3.5 stars. The novella is written in two sections -- it essentially has a beginning and an end, but no middle. The middle, such as it exists, comes through expository dialogue in the second section. Overall, the book reads like a thorough outline for a deeper, more complex novel. The beginning is vivid and addresses the viral nature of revenge as three men, each who have experienced some horror of war, seek to execute a doctor for what they believe are his war crimes. But their act of revenge will have reverberations, as revenge always does. Revenge begets revenge. Violence begets violence. I'd give the first part 4 stars.
The second part is the weaker of the two sections. The two remaining characters from part one sit in a cafe and talk. Then they go to a hotel and fuck. Then they fall asleep. It could have been a beautiful ending, if Baricco had given us a middle section, had let us live in these characters' skins as they grew into adulthood and eventual old age, carrying the trauma of part one through their lives, and then the ending could have been read as a catharsis. But he doesn't, and we only get any of the consequences of part one through expository dialogue, and so at best I can give part two 3 stars simply because I like his writing. But I'm left disappointed because this book could have been so much more.