Feldman's "late" works are the most remarkable. Often spanning hours in length, he transformed the concert into a ritual. "Is music an art form?" he liked to ask. In other words, is music more than just entertainment? His answer was clearly: "Yes".
Feldman's works are not just listened to, they are experienced. They are a mixture of music, performance art, and philosophy. Unlike John Cage, his close friend and mentor, Feldman was not interested in Zen philosophy. But listening to Feldman’s music leads to a heightened state of mind, a kind of musical enlightenment.
I just recorded two of Feldman's greatest works for solo piano: "Palais de Mari" (1986, 23') and "For Bunita Marcus" (1985, 67'). 15 minutes ago, I would've put the probability of seeing an article about Feldman on Hacker News at zero. Bravo.
Feldman's "Rothko Chapel" is a great way to get into his music (written following the suicide of painter Mark Rothko).
Here is part one:
http://www.youtube.com/watch?v=qxSt_w2ODaQ
The story of the Rothko Chapel is well worth reading if you like abstract expressionist artwork (de Kooning, Rothko, Kline, Pollock, etc).
http://en.wikipedia.org/wiki/Rothko_Chapel
Also, I recommend listening to the conversations between John Cage and Morton Feldman:
http://archive.org/details/CageFeldmanConversation1
They talk, drink, smoke in the radio studio. It's all very 1960's but the insight into the lives of great composers is priceless.