They may have perfected playful vocal pop, but Frankie Valli and his Four Seasons experimented freely during the '60s. You can hear the influence of The Beach Boys' Pet Sounds on both the melancholy mood and baroque ambitions of “Tell It To the Rain” and “Heartaches and Raindrops”. And by 1969, the group had staked out a slice of full-blown psychedelia with the surreal, “Hey Jude”-referencing epic “Genuine Imitation Life”.