Recently Tetris Blitz was covered on Pocket gamer on how a 3 year old game still Kicks-ass when it to comes to player engagement and satisfaction.
It's often said in the world of free-to-play development that launching a game is the beginning, not the end.
These aren't boxed products released onto shop shelves, never to be worked on again. These are games-as-a-service that require constant operation and updating, often over a period of several years.
You can read the full article on the recent success of Tetris Blitz on the PocketGamer.Biz