Let me get this out of the way: Tiny Wings is like crack. I used to dream about it at night, and not many games invade my nap time.
Tiny Wings, at the moment is the top paid app on the Apple App store, for good reason. Combining simple pick-up-and-play game mechanics with a great physics engine, you will get hooked once you become familiar with the methods of scoring high.
The game tells a story of a bird with 'tiny wings' trying to venture as far as he can until he falls asleep, using the momentum of the terrain on his path. Essentially, the game uses touch controls to navigate the bird up and down, which will allow you to gain air and speed, the more precise you are in timing the ascent and descent of our bird friend. This timing mechanic is what makes the game so addictive, because if you slide perfectly down three hills in a row, you activate Fever Mode which is like Star Power in Guitar Hero, or Overdrive in Rock Band; where you accumulate double the score, as long as you continue to slide down hills perfectly. In order to get any sort of respectable high score, you need to stay in Fever Mode for a substantial amount of time, so you need to be mastering the art of perfect slides. Luckily the game is lenient enough to make it not incredibly hard to pull them off, and it simply requires reflexes and a good sense of timing, which develops the more you play. After playing a few games, you'll be pulling off perfect slides easily.
The other mechanic that makes the game so addictive is nests, which dictate your overall multiplier throughout all your games, and you need to fulfil certain goals in order to acquire the next multiplier. These nests conflict with the overall goal of trying to gain high scores, because some of these goals are counteractive to gaining a high score (for example: reaching the fourth island without a perfect slide), so you need to prioritize either aiming for the best score you can possibly get right now, or trying to reach higher multipliers for eventual higher scores.
Tiny Wings is great for either a quick two minute playthrough, or an hour marathon, you'll never want to stop trying to get as high a score as possible to compete with the leaderboards. It is recommended that you try and convince some good friends to buy it as well, because you'll gain more out of it if you have someone to compete against.