Dominic Cobb’s review published on Letterboxd:
(Note: not all of these categories need to be filled for a film to be perfect or great)
It's easy to see, now having watched this film all the way through, why many consider it great. It doesn't reach my Greats list, but I understand completely why many consider it to be one of the great films (including Ebert).
Much of the film's excellence is due to Alain Delon. His performance here is absolutely stellar. He acts with a straight-faced dignity, so confident and sure of all his actions, and it truly contributes to the character. The man he portrays, Jef Costello, is a hired assassin, who is seen in this film in a single trip-up, likely one of the only ones he's ever faced in his career, that sets the entire film off: a woman catches him in the act of an assassination. In the moment it is brushed off as he stares at the woman for a second, but it has dire consequences that are reflected throughout the film.
A majority of Le Samourai is watching procedure. The audience observes Jef's habits and the specifics about his character, and his attitudes. He is quick and calm under pressure, and cares a lot about his appearance, as in the opening scene he adjusts his hat specifically, running his hand across its rim thrice.
Subtly entertaining and terrifically engaging, Le Samourai, though not quite great (yet) in my eyes, is clearly a brilliant piece of original cinema, though often relied upon in modern films.