I'm puzzled:Y iPod so popular?

I don't own an iPod or its cousins. Can someone who owns one or knows these gadgets well tell me why iPod is so popular? I've seen ads and they look cool and all, but I don't want to spend a few hundred bucks on such a simple appliance. Besides, other companies have similar offerings. So what does iPod have that others don't? Ease of use? Fashionable coolness? Large music DL library (I heard it ain't free)? I'm really behind on this fad. I'm hoping someone can enlighten me and make me feel the urge.