The Callahan Chronicles are particularly good. Funny. Er, helps if you like puns.

Later yet, I avidly read his book reviews in "Galaxy" and elsewhere, allowing them to influence my paperback purchases for some time after. (I might never have discovered Edgar Pangborn if Robinson hadn't recommended him highly---though it was another ten years before I truly thought I understood "Davy.")

I liked the way he connected events in his created worlds with what happened personally to his characters. (Think of it as, say, when writing one of those old space operas where world-shattering missiles are flung about like silly string---and he'll be be dealing with the life of the guy who has to fire that missile---or the guy it's pointed at.)

I think I grew a little disenchanted with the way and the world the later Callahan stories developed, and also some strong currents in his other work that could maybe be best described as "Resident Canadian." (My political leanings have sharpened considerably since my younger days, and probably my aggrivation and tolerance levels are somewhat lower.)

Still, even some of the later stuff remained good reads. I'd recommend his work to all.