"One" is flat out one of the greatest moments in u2's long and successful road down Rock n' Roll history. It is an incredibly written and produced song, perfectly completed by the emotional and soulful voice of Bono and the amazing guitar playing of The Edge. I feel it is one of the most emotional songs I've ever heard, and along-side "With or Without You," my favorite of all time.
Along with the hit that Axel Rose (of GNRs) said is one of the "best songs ever written," there are other great tracks on this single that make it a must buy for not just u2 fans, but any music fan. "Lady With a Spinning Head" is a simple, great rock song with an addictive chorus and great guitar riffs by The Edge. It was left off "Achtung Baby" because the guitar solo at the end of the track contains parts of "The Fly," which was a hit on that album. But "Spinning Head," in my opinion, could easily have deserved a spot on "Achtung" (one of the best rock albums of all time). I think "Spinning" is one of the best B-Sides U2 have ever released (it's challengers: Dancing Barefoot, Everlasting Love, Summer Rain, Always).
The other two tracks on the single are "Satellite of Love" and "Night and Day (Remix)." The prior mentioned is a cover of a Lou Reed song which is done very well, maybe even better than the original. I never got into this track too deeply but I'm in the minority of U2 fans for sure. "Night and Day" is a remix that sounds like their "Achtung Baby" style, an unexpected surprise to end a classic single.
If you don't have this single and you're a U2 fan, you're missing out. A+++