I play the paid version (ad-free) regularly and thoroughly enjoy it. There are two issues that need to be addressed to be 5-star app:
1) To play a solo game, I have to do at least 6 selections (clicks). 1 for Play in Game Center, 1 to say no to login to Facebook, 1 to Play, 1 to play (more clicks if I want to change computer opponents), 1 to choose the # of cards, and another one if resuming a game. Have the programmers never heard of a settings panel?
2) Playing the hardest level against the robots is no fun. The algorithm results that the computer opponents rarely ever play any cards.