Simon & Garfunkel received criticism at the height of their success. In 1968, "Rolling Stone" critic Arthur Schmidt described their music as "questionable ... it exudes a sense of process, and it is slick, and nothing too much happens." "New York Times" critic Robert Shelton said that the duo had "a kind of Mickey Mouse, timid, contrived" approach. According to Richie Unterberger of AllMusic, their clean sound and muted lyricism "cost them some hipness points during the psychedelic era ... the pair inhabited the more polished end of the folk-rock spectrum and was sometimes criticized for a certain collegiate sterility." He noted that some critics regard Simon's later solo work as superior to Simon & Garfunkel.