The first few games were extremely frustrating, as it takes a while to figure out how to prevent the AI from stealing your kingdom. Despite the tutorial, highlighting the cards you can use to defend yourself would have made things a lot clearer.
Implementation-wise, I know that the board looks tiny on the iPhone, but dont worry, its easy to place tiles down on the board at the correct location. Picking them back up is harder (you need to zoom, and even then), but you dont need to do that nearly as often.
No complaints about the AI yet.
Gelisam about Reiner Knizia Tigris&Euphrates, v1.2