I first read Titan, and had my mind blown. Then I found out about Steel Beach, and the Eight Worlds series and his collections of short stories, The Persistence of Vision, Blue Champagne, The Barbie Murders...
Its kind of sad, in my opinion that he's mainly known, if he's known at all, for Millennium, which I think is among the weakest of his work. I found his dealings with the future tech of virtual immortality, cloning, braintaping and AI collapse in Steel Beach to be pretty profound. Hotline dealt with a lot of the same issues, where Golden Globe focused more on the just living a life that can be measured in centuries, and how even then, your past can come back to haunt you.
Anyway, all in all, an author that I've always enjoyed; he makes me think.
TLDR: If you haven't read anything by this guy, go do it now :D