Flappy Bird provides solid evidence that simply tuning a game well can be far more important, in terms of the player’s ultimate enjoyment, than adding clever mechanics or beautiful art.
Flappy Bird is dead — but brilliant mechanics made it fly | Technology | theguardian.com
It’s interesting to see game feel and game tuning getting more and more attention due to comments like this one from Bennett Foddy. See also Jan-Willem Nijman on Nuclear Throne.