The story of Shamus seems to be loosely based on Raymond Chandler's The Big Sleep. Burt Reynolds is in the Humphrey Bogart role, and he acquits himself well playing the Philip Marlowe of the chewing gum generation. He doesn't take himself too seriously, is less sarcastic than the forties version and there are quite a few good laughs to be had.
Shamus is remarkable for reflecting the period it was shot in. The directing and the cinematography are very good. I also liked the musical score. There are quite a few nicely stylized action scenes on real locations in dock areas. Dyan Cannon gives her usual solid performance and wears clothes today's fashion designers will be very interested in. Her character's apartment in a high rise on East River must be the "dernier cri" of 1973s interior decorating: prints of Vasarely and Miro, steel frame chairs with white leather cushions, lamps with huge chrome bowls etc. etc.
This movie, a bright child of its time, is well worth preserving.