"Opus 17" was the first hit with new full-time bassist and bass vocalist Joe Long.[4] The title meant that this was the 17th single released by the Four Seasons.
As was the case with another Linzer-Randell contribution to the Four Seasons catalog, "Let's Hang On!", "Opus 17" features a rhythmic vocal hook within each verse, but, unlike in most Four Seasons singles up to that point, the song uses very little falsetto from Frankie Valli other than in the closing coda; by 1966, Valli was tiring of singing falsetto and, over the next several years, would begin singing music that did not require it.[5] The song begins in F-sharp major, and goes up by half scale, until it reaches the coda in B major.
Billboard praised the "excellent vocal and instrumental production."[6]Cash Box described the song as a "pulsating, blues-soaked romancer with an infectious, Seasons-associated repeating, danceable riff."[7]Record World said it "gets rolling like mad and then modulates upward."[8]