At first I was exited about another Mahjong, then I saw the price. $20 is what the other high-end Mahjongs go for, so I'm expecting something pretty slick, which this app is not. This seems to be a Flash app (Director Player) mascarading as a Mac OS X app. Being such, it has the same problems that java apps have, meaning it's slow on response, and does not have a standardized interface (no menus except basic app menu to quit).
Several times I got a "Director Player Error" message with "Script error, continue?". If you click no, then app quits ASAP.

Burning Monkey is more stable and fun. Give it a go for the same price.