Jack is an unqualified genius in my book. I love his early playing with Miles, Chick and Lloyd, but his trio work with Jarrett and Peacock is probably my favorite stuff. I was lucky enough to catch him live with Pat Metheny, Ornette, Charlie Haden and Denardo (?!) on the Song X tour at the time. Great show and a chance to see Jack in a really different head space!
Jack, to me, is the least-cliched and most spontaneous jazz drummer ever. It seems like every phrase he plays hatched directly out of the moment, fully-formed and inventive. To be able to compose so musically behind the kit, without just getting into the rut of repeating oneself and resorting to re-arranging "licks," is something I aspire to. I don't think anyone does that better than Jack.