How old are you?
Cuz I watched it in my mid-teens and thought it was just okay.
Then, when I was twenty, living on my own in a big city, and working the night shift, I re-watched it. That's when it became my favorite movie ever (barring my optimistic days, then it's behind Magnolia).
It has a kind of lonliness, and rage, and sick sexuality about it. Thinking you could "help" others when you can't even help yourself. The story, acting, and shots are all perfection to me.