Made by Trevor Van Meter, Jason Krogh, Vas Kottas and Brian McBrearty, Fly Guy is easily one of the best webgames available. The graphics are stylish, the animation is fluid, the sounds (often overlooked in webgames) are great and the gameplay is easy enough to make it interesting for anyone.
No, it's not 'easy to learn and difficult to master'. Unlike most games appealing to casual players, it's not a puzzle and it's not contained on a single screen. In fact, exploration is key to this game. The pleasure is flying around with the character and interacting with the objects and other characters.
Exploration is usually a turn-off for nongamers, but that is not the case for Fly Guy. The navigation scheme, combined with the graphic's simplicity, gives the player the illusion of an infinite space - which turns out to be actually quite simple. Because of the amusing animations, the player is also compelled to see how the character interacts with every other entity of the environment - and by doing so, the player wil fly higher and higher towards the end of the game.
Of course, the player is not informed of that ending when the game starts, as it could make him feels as the goal should be to reach it as fast as possible. In fact, by the first time you reach the end, you will want to restart it and make sure you've seen it all. Other than that, the only replay value are in the random comments made by a floating guru) and in the pleasure of flying around and watching the interactions again and again. It's enough to make you go back and play it every now and then.
Overall, the fact there's no punishments and pressure to finish the game (or to do anything else than explore it and play around) gives it a nongame, toy-like quality - even if there is a linear path and an ending involved.