He's one of the legends in the field, having written many classic works, but unfortunately I've had to take everyone's word for it.
My sole experience with Vonnegut was an aborted attempt to read Galapagos back in the early 80's. Couldn't stay interested in it. I'm thinking perhaps I should have tried something else first instead, Slaugterhouse Five perhaps. I've led such a sheltered life.
Anyway, I know he was one of the giants, and the world is a lesser place for his passing.