I wasn't a big fan of the album but I adored God only knows, and I still do.1 It's one of my top ten favorite songs. The song ranks at #25 in Rolling Stone's 500 Greatest Songs of All Time. Paul McCartney, who played for another popular group in the 1960s, says that God Only Knows is his favorite song of all time.
The music was written by Brian Wilson2 and the lyrics are by Tony Asher. I don't know very much about music so you'll have to read the Wikipedia article to appreciate why so many people admire Brian Wilson. Carl Wilson, Brian's younger brother, sings the song.
The video is from Good Timin': Live at Knebworth England 1980. It's one of the rare occasions after 1965 when all six Beach Boys (Brian Wilson, Dennis Wilson, Carl Wilson, Mike Love, Al Jardine and Bruce Johnston) are together. I think it's the only video where Brian Wilson is playing on God Only Knows. (That's him on the piano.)
I never saw a live performance of the original Beach Boys but I've seen the Mike Love version twice.
1. Some atheists will never like this song because it mentions God. That sort of thing doesn't bother me. I can still sing God Save the Queen and the Canadian national anthem without batting an eyelash. There are much more important things to fret about.
2. I just read in the Wikipedia article that he was inspired by the Lovin' Spoonful song You Didn't Have to Be So Nice. That song is also one of my personal favorites but I never twigged to the similarity until now.