"One Sweet Day" is about losing a loved one, and eventually seeing them, once again, in Heaven one day. Both Mariah and Boyz II Men wrote the song about specific people in their lives to include sufferers of the AIDS epidemic.
You prefer Touch My Body and Thank God I Found You?
Apart from TGIFY (which is hideous) "One Sweet Day" is the only song by Mariah that I have come to truly hate. Pretty much every other single that she has released, even "Heartbreaker", is either great or pretty good.