Many Faces of Go version 12!
First, it's been updated to version 12, and mixes in the recently developed Monte Carlo Tree Search (MCTS) algorithms by Sylvain Gelly, et. al, enabling it to play as strong as 2 kyu on single core machines. That's 3 dan, in 9x9 games!
Second, it won two gold medals (for normal and 9x9 play) at the 13th World Computer Game Olympiad (2008) in Beijing.
Third, the graphics are more visually appealing than the ancient, two dimensional Windows versions that have been floating around for years. This is a small point but it counts a lot. The board now shows a kaya grain and the stones mimic slate and shell. The effect is understated, but it looks right — except under Wine, where the stone shadows are white instead of black. Of course, Macintosh OS X still sets the highwater mark for best Go graphics on any computer, bar none; on Windows, CGoban 3 and PANDA gGo also have attractive board graphics, IMHO.
And fourth, it runs out of the box under Ubuntu Hardy, in Codeweaver's CrossOver Linux Standard!
[Update: The Trading Centre in the U.K. uses CopyMinder, a "call home" type copy protection nanny, which does not play well with Linux, at least on my system. I could not run the full-feature, time-expiring demo because of CopyMinder.]
The version 12 evaluation copy (at Smart-Games) does NOT expire, but it has a few disabled features — e.g., you can only play handicap games by registering, computer opponents stronger than 18 kyu require registration, fuseki study halts after a few stones are placed, Go problems are really simple, etc. One thing you can do is replay those games of Shusaku which are included in the library. A standard, reasonable demo, easily paid for and registered at Smart-Games.
Five stars out of five.