First off, this isn't mahjong, nor is it kyodai (which is the game most Windows computers come with that is labeled "Mahjong"). Sure, it uses Mahjong tiles, but that isn't enough... if I made this exact game with different coloured golf balls, it wouldn't be golf, either.
Perhaps the biggest problem with this game is the lack of instruction; the player is simply thrust into the game with a series of mahjong tiles laid out in front of them and four buttons to the left of the board. The buttons aren't even labeled, so if the player happens to get curious and click the button on the top after they had gotten decently into the game, the whole board resets. Sound effects are minimal and repetitive, and music is non-existent. Lastly, never use the scroll wheel in a Flash game, as it scrolls the browser window as well as performing actions in-game.
I can't give this game a good score, simply because there is so much missing from it. I couldn't find any bugs with it, but sometimes that isn't enough.