Monument Valley is a calm puzzle. You have to guide the way for a little princess through geometric mazes that will challenge your perception. 10 levels can be explored within an evening. 8 additional level are offered as in-app purchase. For that reason the app seems a bit expensive. Nonetheless, it is a beautiful game with surprising perspectives and optical illusions.
Osmos HD. There won’t be very many games in my collection. Here is one exception. Osmos is a contemplative, dynamic, strategic game. By emitting matter you push a little amoeba into the opposite direction – sometimes you control a planet or star. Get big, eat the others. Do not get eaten or absorbed. Beautiful graphics. The game is also Game Center enabled, which injects a bit of intelligence and intent into the opposite cells.