Well said, Mick! "Sweet Smell" has always gotten recognition from critics--including those whose view of Tony Curtis's acting chops was formed by those dreadful biblical and medieval roles he took. He and Lancaster slayed 'em in "Sweet Smell."
Another of my candidates for underrated films is "Seconds" (Frankenheimer, 1966). It was panned at the time, but today has something of a cult following. IMO, it's Frankenheimer's masterpiece--an eerie, scary story of middle-aged angst and transformation that says a lot more about "success" than is apparent at first. Outstanding performance by John Randolph, Francis Reid, Jeff Corey,
Wesley Addy, Murray Hamilton, Khigh ("Wo Fat") Deigh, Salome Jens, and, yes, Rock Hudson in his finest role. Terrific camerawork by James Wong Howe. I've watched it close to 500 times. Anyone else familiar with "Second"?