One year after releasing their gritty, garage-rocking self-titled debut, the Grateful Dead returned with a massive evolutionary leap: the sprawling, psychedelic Anthem of the Sun. Outré epics like "That's It for the Other One, Pts. I-IV" alternate between acid-rock excursions and atonal avant-gardism inspired by keyboardist Tom Constanten's experimental background, while trippy tunes like “Alligator” get a good coating of grease from resident blues wailer Pigpen.