I learned from Wikipedia that Truffaut loved Rififi, saying that "out of the worst crime novels I ever read, Jules Dassin has made the best crime film I've ever seen."
(Truffaut trivia: Spielberg cast him in Close Encounters as a scientist. The other scientist was played by Bob Balaban, who directed one of my favorite creepy films, Parents. I had a celebrity sighting of Balaban in an ice cream store a few summers ago. Small world!)
A lot of reviewers (e.g. Ebert) say that Rififi invented the modern heist genre. It doesn't feel much like Ocean's 11, though. The hero, "The Stephanois", is not particularly likable; near the beginning of the movie, he beats his ex-girlfriend with a belt. The action in the film is not stylized, but rather rough and tumble (which is a loose translation of the word "rififi"). The actual heist occurs in the middle of the movie, and it's almost a half-hour of silent, efficient thievery -- no humor, no surprises, just four men doing a thorough job.
Once the heist is done (spoiler warning), there's still almost an hour of movie left, in which "The Swede's" son is kidnapped. The Stephanois spends the rest of the movie getting him back, with most of the cast dying along the way (including Cesar the safecracker, played by the director). The movie ends with a surreal scene where The Swede's son cavorts in a car as he's driven home by The Stephanois who is bleeding to death from a gunshot wound. It's hard to tell if the careening shots of tree branches and tiny Paris streets are supposed to represent the viewpoint of the distracted five-year-old or the dying thief. Either way, it's a powerful finale.
The trailer doesn't really do the movie justice:
Rififi is worth seeing if you have any affinity for heist movies or film noir. See it before Al Pacino remakes it.