Kanye West is a talented artist and autotune songs like "Heartless" are great. The problem of "Only One" is, as it was the case sometimes in Kanye to frantically artistically. A continuous piano playing that without any drums and also almost the only "beat" is heard throughout the song, is already getting used to for a rapper. In addition, not only the sound but also the vocals are often so overloaded that it just hurts. If you are eager to convey a lyric sad, you should make it a little high and the fact that Paul McCartney sits at the piano, also improves nothing.