The unreleased album SMiLE by The Beach Boys. It's been regarded as one of the greatest "what-ifs" in music history. It was supposed to be a follow-up to the equally legendary Pet Sounds, which itself made it to the top 5 in numerous "greatest albums of all-time" lists. Brian Wilson called it "his teenage symphony to God" and it would have been the group's magnum opus, probably knocking Pet Sounds out of the apex of musical influence. The album cuts were technically complex music pieces and even suites, some said to be even more experimental than the songs in its precursor. It was also said to be the quintessential American response to the British Invasion in both form and content, tracing the history of America through musical experimentation.
"Good Vibrations" was to be the carrier single from the album, released and peaking in at #1 on the singles charts in 1966. When the whole SMiLE project fell apart, it was included in the album that eventually took the burden of following in the footsteps of Pet Sounds, Smiley Smile, much to Brian Wilson's disapproval. Smiley Smile was nothing more than an ill-fated attempt to salvage the failed SMiLE project.
Ultimately, it was conflict between members of the band (it is said that Mike Love loved the music but hated the lyrics), Carl Wilson's drafting into the military despite his conscientious objections, and Brian Wilson's increasing drug use and mental instability that brought production of the album to a crashing halt. Some songs were scattered among bootleg recordings, others were incorporated into later Beach Boys albums. 37 years later in 2004, Wilson and his touring band would resurrect the project under the name Brian Wilson's SMiLE. The music remains of course, but how sweet would it have been with the vocal harmonies of the original? With Carl and Dennis Wilson gone forever, we'll never know.