Various other artists have contributed to the band's albums, notably Queens of the Stone Age front man Josh Homme, Pearl Jam singer Eddie Vedder, and Soundgarden guitarist Kim Thayil.
Matt Diehl of Rolling Stone said, "Declaration of Conformity suggests that these Soundgarden expats have left the Seattle sound behind for trippy psychedelia that recalls such '60s freak icons as Syd Barrett and 13th Floor Elevators.
Chris Handyside of Rolling Stone said that "amid all the fuzz and minor chord bombast is an edgy, hard-rock post-millenial [sic] tension.
David Fricke of Rolling Stone said Wellwater Conspiracy "upgrade the fragrant eccentricity of vintage U.K. flower power—spaced riffing, spiked-afternoon-tea lyrics—with modern muscle.
Notable appearances included keyboardist Glenn Slater of folk rock group The Walkabouts, guitarist Kim Thayil of Soundgarden, vocalist Eddie Vedder of Pearl Jam, and vocalist/guitarist Josh Homme of Queens of the Stone Age and Kyuss.