There are three different "sizes" of Hong Kong Mahjong. Here is a simple demo for the 800x600 program. The two larger versions are identical except that the graphics are optimized for larger displays. Sorry, there are no demos available for the 1024x768 and 1280x1024 versions, but there are screen-shots on our Features page.
This demo is limited to a single round each time you run it, but it does allow you to preview every feature and see that this indeed is real Chinese mahjong.
Try it, and have fun!