Musical theater often gets a bad rap for lacking the depth and complexity of other genres. In her 1992 book, Art Isn't Easy: The Theater of Stephen Sondheim, Joanne Gordon describes how this attitude toward musical theater evolved and Sondheim sought to shake things up...
"The reasons for the musical’s disrepute are many. In its infancy, in the early years of the 20th century, musical theatre was unsophisticated...The simplistic moralism, the naïve optimism, the noble hero and simpering heroine were adopted, unaltered, from the nineteenth century melodrama. The commercial success of these pieces encouraged their fossilization into a predictable pattern... [and] the musical was viewed solely as a commercial commodity.
The evolutionary progression of the musical from Showboat to Rodgers and Hammerstein’s Oklahoma! is well documented in histories of the American musical. The form changed and became increasingly complex. Integration became the key word as Rodgers and Hammerstein wove the texture of song, dance, and plot closely together. Yet despite the fact that such themes as racial prejudice (in South Pacific and Finian’s Rainbow, for example), marital disharmony and infidelity (in Carousel and The Most Happy Fella), and capitalist venality (in Allegro and How to Succeed in Business Without Really Trying) were introduced, this kind of theater retained an essential naiveté. The musicals of the forties and fifties were escapist in that they transported their audience into a larger-than-life world where emotions were expressed in melody and the evening capped with a reassuring reprise at the final curtain. The climate of progress and promise that prevailed during the creative period of Rodgers and Hammerstein’s career no longer existed by the late 1960s. From that point on, for an artist in the commercial theatre to comment on, or attempt to change, prevalent attitudes has been an invitation to financial disaster and obscurity.
Sondheim and his collaborators [instead] choose both complex subjects and consistently experimental techniques, and their musicals begin after the traditional happily-ever-after has run into trouble. In an interview with Hubert Saal of Newsweek, Harold Prince explains his and Sondheim’s commitment to “truth” in the musical theatre: “I work in the theatre, not in the musical theatre...Who says to be entertained means to be tickled?...I think it’s more stimulating to be upset. I try to be part of what I want to see. And I go to the theatre to see a little blood drawn.”
Sondheim has redefined the genre and, as a result, the gulf that separated “serious,” “legitimate” theatre from the musical theatre has effectively been bridged."