Oodles of variety of layouts and tiles with endless combinations available to customize. Easy to see on the retina display -- no need to constantly zoom in and out as with other mahjong apps. The pithy, sarcastic fortune cookie messages at the end of each game are hilarious and a nice touch. My only quibble, and it is a minor one, is that it shuffled the tiles a bit better. Quite often the same tiles are adjacent to each other or bunched within the same area of the layout.
VioletNinja about Shanghai Mahjong