I subscribed for the first time in 2005 after I saw Lewis Lapham on LinkTV. He was the General Editor then, and described how the magazine was mostly independently funded to avoid the influences of, oh, forces like oil, telco, etc. etc.
It does have some fiction and poetry in it, but the heart of the pub is people with their heads (generally) in the right place who do investigative analysis of political and cultural trends and events. They have taken the Bush admin down a peg or two, and they are on the radar those minions (Karl Rove recently wrote a complaint letter to them).
And the Harper's index is almost worth the price of admission (subscription admission that is).