[Betonov]

Originally Posted by Skybird

And a whole quantum leap of variations more than in chess, I think. Extremely difficult for computers to calculate, since the variation tree is extremely wide.

Yep, wiki says:

There is significant strategy involved in the game, and the number of possible games is vast (10^761 compared, for example, to the 10^120 possible in chess), despite its relatively simple rules.

Despite ?? It's because it's simple rules. Less rules, more options.

and:

The game complexity of Go is such that describing even elementary strategy fills many introductory books. In fact, numerical estimates show that the number of possible games of Go far exceeds the number of atoms in the observable universe.