Pretty much everything about the song. It's magic to me.
I love the opening riff. I love the desperation in his voice. I love the clalm of the verses, met with the roar of the chorus. I love the way he sings the line "like a fool, I fell in love with you, turn my whole world upside down". I love the emotion of it all. It's one of those songs that just sound very real, like it was written about something very real.
I also love the beautiful piano ending.
I guess if I had to pick a single favorite moment of the song, it would be that line I quoted above.