For a while now, Angry Birds has been one of the top selling games on iTunes. There’ve been many articles why this game has been such a success, in particular this great breakdown , but I thought I would share the reasons why I like this game so much.
The reasons why I like Angry Birds
Even though you still need your other hand to hold the iPhone, you can play the game fully with one hand. This is particularly handy when you are on the subway or bus. One hand is firmly holding the iPhone and the other hand can easily reach a pole or wall if you suddenly become unstable. In games that require two hands, both hands are positioned for the game rather than holding the iPhone. If the bus suddenly hits a bumpy stretch, you have to stop playing, reposition one hand to hold the phone more firmly.
Angry Birds allow users to easily decide if they want to leisurely play though the levels or challenge themselves by trying to obtain 3 stars (or feathers). I usually unlock all the levels then go back to obtain 3 stars.
There are many articles analyzing the UI design. I agree with most of them. 🙂
Nothing is more satisfying then throwing items into blocks and watching them smash. 
I really love the intuitive game play and controls. The slingshot, aiming, and power are all very intuitive in their design so anyone can understand how to use them and improve on getting better. The concrete, wood, and ice blocks are all obvious for users to understand that some are stronger them others. The helmet is a great way to introduce “stronger” enemies without complicating the game with more characters.
When birds are introduced to the user for the first time, they are not forced to read the manual. Instead, the game provides a short introduction video and starts users off with easy levels to learn the characteristics of the new bird. 
Unlike time killer games that have no long-term goal – and simply send the user back to “level 1” when restarted, Angry Birds challenges users to keep playing to achieve a long-term goal. This goal could be unlocking all levels or obtaining 3 stars, but it keeps users to continue playing. 
This is the perfect game for playing on the subway or bus. It doesn’t require uses to pause if interrupted, levels can easily be restarted, and as started before, only requires fingers from one hand to play. It can be closed and restarted at the very point the user left the game.
And that is why I like Angry Birds.