To Have and Have Not has a reputation as Hemingway's worst book, and it is the worst of his books that I have read. The book is experimental. At first it is influenced by noir writing such as Hammett and Chandler. Later it moves out of telling a narrative and starts telling the stories of multiple people whose lives intersect more or less. There are occasional moments of the Hemingway magic, but bits of it fall flat and it doesn't work together that well as a whole.
That being said, the fact that Hemingway was still willing to experiment is admirable and Hemingway at his worst is still well worth reading and better than most stuff. It's not the place to start with Hemingway, but if you like really like Hemingway, its worth your time, but don't get your expectations too high.