I never realized that Go was more complex than chess in terms of number of potential moves throughout the game.

From the Wikipedia article on Go:

The area of the board is very large (more than five times the size of a chess board). Throughout most of the game, the number of legal moves stays at around 150–250 per turn, and rarely goes below 50 (compare chess, where the average number of moves is 37). Because an exhaustive computer program for Go must calculate and compare every possible legal move in each ply (player turn), its ability to work out favorable lines of play is sharply reduced when there are a large number of possible moves.