Robert Roten in Lariat.org:
“With a Friend Like Harry” is a complex psychological thriller about an old high school classmate who is more than a little strange. This French film with English subtitles is a little similar to some Hitchcock films like “Strangers on a Train.” It starts out with an average guy, Michel (Laurent Lucas), his wife and kids on a very unpleasant car trip on a very hot day. The kids are screaming in the back seat and one of the kids is repeatedly kicking the back of her father's seat while he is trying to concentrate on driving. There is no air conditioning in the car, and the car itself is making a lot of noise. Michel decides he's had enough and decides to go back home rather than continue on the trip to his parent's house. Then he meets an old high school classmate in a public rest room. Harry Ballestero (Sergi López) remembers Michel very vividly, but Michel has forgotten Harry altogether. It turns out that Harry is a big admirer of Michel's writings in some high school publications. He has even committed one of Michel's poems to memory. When he finds out that Michel has given up writing and he sees how family concerns are weighing on him, Harry decides to “help” Michel free himself from his worries and get back to writing. Harry and his girlfriend, Plum (Sophie Guillemin) stay at Michel's country home and Michel begins to learn more about Harry. He finds out that Harry is used to getting exactly what he wants, exactly when he wants it. He will do anything to get what he wants and he will not compromise. Harry is also rich, having inherited his father's estate, and can be quite generous. Harry buys a car to replace Michel's worn out vehicle. It is just part of Harry's plan to help Michel. Not all of Harry's plans are so benign.
The complexity of the plot has to do with the way Michel is changed by Harry.
More here. (Note: I will periodically post reviews of older films that I have recently enjoyed.)