the area of the board is very large (five times the size of a chess board) and the number of legal moves in progress at any time rarely goes below 50. throughout most of the game the number of legal moves in process stays at around 150-250; computers have difficulty distinguishing between good and bad moves.
whereas in most games based on capture (e.g. chess, checkers) the game becomes simpler over time as pieces disappear, in go, a new piece appears with every move, and the game becomes progressively more complex, at least for the first 100 plays.
unlike other games, a material advantage in go does not guarantee a simple means 