Go is an essential game: its rules unfold flawlessly from the concept ... well, almost.
It is also one of the oldest and one of the most sophisticated games known to man - a rare combination. It has an immense literature, now readily accessible through the internet. It has an extremely small marging of draws and has long eluded attempts to formulate evaluation functions that would allow programs to perform more impressively. With the rise of Monte Carlo based evaluation programs have made such progress that it is safe to say Go will eventually succumb like any other abstract strategy game.

Where there are thousands of chess variants, the number of Go variants is very small. Chess of course allows this multitude because there's virtually no limit to creating different pieces with different powers on different boards with different rules. Go in its simplicity hardly allows such changes.