Everything that the other reviewer said. I have watched this film many times. Wonderfully paced, casting perfect.
From the get-go, Don Segal's version of the Hemingway story is brash, sexy and violent. Marvin and Gulager, as the no-nonsense contract killers, open the story by dispatching ex-racing driver Johnny North (Cassavetes) in a hit that pays them $25000. Marvin's character, Charlie Strom, ruminates on what makes the hit so lucrative, and he and his sidekick Lee, played by Gulager decide to investigate by paying Johnny North's race mechanic played by western stalwart, Claude Atkins, a visit.
From then on the story is told in flashback. Enter, the incredibly sexy Angie Dickenson, as the dame who who wants North but is owned by Ronald Reagan's character, mob boss Jack Browning - using North as their driver, this is the gang (Dickenson, Reagan, and Norman Fell) that robs a mail van for a million. After a lot of double crossing Strom gets to Jack Browning and the money, only to be taken out himself.
The movie is brilliantly paced. The dialogue is spot on, and the acting first rate - Marvin, Gulager, Dickenson, Cassavetes, Reagan, Fell and Atkins are a brilliant ensemble cast. The cinematography is perfect, using bright primary colours, and inventive camera shots. Siegel's direction is solid without being too flashy, making the most of the limited budget.
The movie is way ahead of its time - you can see hints of Pulp Fiction in the characters of the two hitmen and the overall style of the movie. Whilst the story may not be particularly different from many other noirish movies, the way Siegel has put it together creates a modernist crime caper, with a seething undercurrent of sex and violence.