Easy question, easy answer.
I still see lots of this, but the worst fault is: not embedding or linking to a sample of the music. The Internet is RICH, and humans love to take advantage of our senses!
I know some web music reviews are actually copies of previously printed material, and we can't feasibly embed music into paper. Yet.
But still,
it takes a few seconds to search Amazon, YouTube, iTunes Store, IMEEM, lala, etc. for a clip — or someone can build a better utility to link 'em. And if you got a promo from a band or their record label, they should help you out.
Put it in context:
your words are colored by your experiences and without the common reference point (the music), is a map without a destination. Even if your writing strives to be its own pocket universe, as some Pitchfork staff are wont to do.
Text which speaks about but lacks a link to supporting sonics and imagery is absurdly useless.