Damn this song is good.
Killer bass line. So important to a Soul/Funk number. This one is constantly moving, not repetitive, doesn't ring out so much that it covers up what else is going on in the song, and even though it is doubled at various times by other instruments (trombone, piano, etc.) it holds it own through the whole song. Honestly, you can listen to just that line and groooove.
This is a well produced song. You've got piano, strings, electric guitar, brass, drums, that amazing bass line, backing vocals, and what was destined to become one of the most known voices in the Western world, and you can hear all of it. The balance is perfect. This is the first song the Jackson 5 did with Michael on lead vocals, and it was the first of four number one hits in one year. Lyrically, as the book points out, this may be the most upbeat unhappy song every made. The singer has realized they have made a mistake, and let the love of their life out of their life. But the music never lets you focus for too long on this downer of a theme.