Reigns is absolutely brilliant, simple interface but great writing and humour, amazed nobody has mentioned it yet. Also the only permission it asks for is network access and it doesn't show ads. Well worth the price of a pint.

As a general rule most things published by Devolver Digital (Reigns publisher,) are pretty good. I have Luftrausers on PC and if the touch interface is any good that'd be a great time killer too.