Among his works are The High Mass, a Requiem, concertos for flute, guitar, piano, and cello, and the 2001 opera, Jeppe: The Cruel Comedy on a libretto and originally directed by Claes Fellbom, who commissioned the work for the centennial of the Swedish opera company. Fellbom translated the opera into English and directed its first production in that language at Indiana University in February 2003. In 2006, Sandström's Ordet - en passion was performed on 24 March in Stockholm. A number of his works are inspired by significant choral works by Bach and other composers, but reinterpreted in Sandström's very personal style. These include a set of the six Bach cantata texts in Bach's structure (double choir plus four-part chorale), a reinterpretation of the text of Handel's Messiah commissioned and premiered by the Oregon Bach Festival in 2009 and also performed at the Rheingau Musik Festival that year, and works by Purcell.
His work draws on ideas from modernist music, minimalist music, jazz, and popular music. Indeed, in Act II of Jeppe, the chorus sings the line "O Lord, Won't You Buy Me a Mercedes-Benz" in harmony based on the original Janis Joplin melody. He has recently become interested in Tejano music and has been working with incorporating that idiom into his work much as composers of Romantic music collected folk music and incorporated it into their works.