Lyrics

Songs with lyrics are very different from instrumental pieces.  It's an entirely different kind of experience.  Apples and oranges.  Ostensibly, they seem closely related, but no.  They're different beasts.

Singers form a relationship with listener.  ...This is, of course, why the singers in bands always get the most attention: it's the singer to whom we are relating, not the band.

Once that relationship is there, by the way, the music becomes secondary.  The first time I listened to NIN's With Teeth (the album, I mean), I thought it was boring and cheesy rock music.  ...But I have a long-standing relationship with Reznor, ever since Closer tempted me into buying an album that was way beyond my comfort zone, back in '94.
As a result, I gave the album a few chances, and soon it was like I was listening to an old friend.  The music didn't matter as much.  Of course, after a few more listens, it became an album that I couldn't stop listening to.  ...I went through a month of having that album on loop.

His new single (Discipline) appears to be doing the same thing for me, too.