This movie looks old and is sometimes a bit zany, but even if it can't have the same impact than 30 yrs ago, it is still worthy of a viewing. It's fast-paced psychopathic killer movie of the kind that later became so popular till nowadays. The dialog co-signed by Francis veber (La chèvre, le dîner de cons, les fugitifs, etc ...) that is the actual record-man for the number of movie that have been remade by Hollywood, are great and funny. As for the music made by Ennio Morricone, it works great with the movie (for instance the sequence in which Minos (the killer) is tracked up to the Galeries Lafayette's attic by the Comissaire Letellier (J.P. Belmondo) is thrilling partly because of the music and the ambiance). Notice the bit of humor when we can hear as Belmondo chase the killer in the Galeries Lafayette, the woman's voice of the advertising that says in French "there is always something happening in the Galeries Lafayette". As I said, it is a fast-paced movie, it also has a lot of action and Belmondo uses it to show his athletic skills, not using a stuntman to do the job. Belmondo is great as the bad-ass cop with a cynical sense of humor.
I recommend you to check this movie out while keeping in mind that it looks old and there are some awkward moments due to its date of release (guns sounds like firecrackers).