For this one I have already been hooked on Candy Crush Saga. I also enjoy Farm Heroes Saga by the same company. Candy Crush Saga becomes insanely difficult with each passing stage while Farm Heroes Saga stays pretty evenly challenged when you get past the first few introductory levels.
I tried Temple Run and found it to be horribly frustrating. I kept dying within a matter of minutes, and never got very far at all in the game. I just don't have the quick reflexes to keep up with the constant moving, and directional aspects of the game.
Words With Friends is one I have played off and on for over a year. I play with a few people from work. This one really helps to build vocabulary and also challenges you to make the most of double word, triple word, double letter, and triple letter scoring areas. If you don't, and you are playing a good opponent, it will be hard to win. I enjoy playing defense most in this game. If I only get a dozen points on a triple word score, who care. My opponent could have gotten 30 or 40 points, and I have just limited what they are able to play.
Frogger Free and Bubble Mania are some I will check out in the future.