I've lately been on a weird Mahjong kick and I don't mean the tile matching game, but the real 4 player game I think best crudely.
If you simply search for "Mahjong" in the AppStore the results are usually pretty depressing with the VAST majority being simply the tile matching games and of the few that are of the actual full game, most were in Chinese/Japanese only.
What I don't think I fully comprehended until getting into this search is how different each country's take on Mahjong is. While they all share the basic concepts of making sets of 3/4 of a kind or runs of 3, the size of your hand and how points are scored for the winning hand can really vary.
Here is my current top 3 (all are localized in English):
Mahjong Mobile (Japanese rules)
iGame 13 Mahjong (Hong Kong rules)
iGame 16 Mahjong (Taiwanese rules)
And I plan to get my first set from buychina. Is that a good idea?