Here's Murray Campbell, one of the leads in IBM's DeepBlue computer that beat Garry Kasparov, on the difference between Go and Chess:
I don’t play Go, I’ve only played a few games in my life, but I certainly know a fair amount about it. Both games are immensely huge and once you get past 10 to the hundredth power, 10 to 120, 10 to 170 [in number of possible positions], they’re all just immensely huge, very complex games. But Go has the characteristic that wasn’t true in chess, that it’s very difficult to evaluate a Go position just by looking at it. A medium-good chess player like myself can sit down and in a few hours probably write an evaluation function that is pretty good at evaluating chess positions — nowhere near grandmaster level, but it’s good enough that when you combine it with the search it produces very high quality play.