The large number of reviews tossing this in the trash bin as an overwrought 1960s period piece, or inferior when compared to the Pierce Brosnan/Rene Russo remake caused me to find the DVD and take another look.
The problem with the 1967 film is that, unlike most films made today (including the remake), viewers need to think and connect the dots; and, there isn't always a "right" ending with all details neat and tidy. This is still a classic of the caper films, with McQueen giving the definitive performance of his absolute-cool image, and Dunaway as the Joan Crawford of the Virginia Slims generation.
The then-innovative parts of the film, including the multiple split screens and the repetition of the theme song with Noel Harrison look dated (and the split-screen is only effective on the big, big screens of the 1960s-era theaters), but the chess game is still the most-seductive bit of film where all the clothes stay on and nobody talks.
Listening to director Norman Jewison's commentary on the DVD is enlightening. The split screens were indeed a timely gimmick (Jewison and the producer saw the technique at Expo '67 in Montreal), and his explanation of the last scene in the cemetery gives a good insight as to how he aimed the film in general.