Though the Dutch prog rockers Focus would pull an about-face toward commerciality on their next record, Hamburger Concerto is the peak of their progressivism. The 20-minute title suite that occupies the album's second half is Focus at their most musically sophisticated, seamlessly blending rock energy and classical-flavored themes. Flutist/keyboardist Thijs van Leer and guitarist Jan Akkerman are at their most inventive on the rest of the tracks too, from the Renaissance-era flavors of the acoustic-based album opener "Delitae Musicae" to the frenzied, fusion-tinged organ-and-guitar action on "Harem Scarem."