At first glance, you might think I'm a little wacky for suggesting this Flash game from Funyamora.com in Japan. Bubble is cute and sweet, almost sickeningly so, and offers very simple gameplay mechanics. You control a floating spirit by using the arrow keys to catch bubbles that rise up out of the ground and float into the sky. You might even be thinking that you could build such a game yourself, and you'd probably be right. There is nothing very complicated going on here.
What I think is so special about this game is the care that went into balancing the gameplay, thus providing 10 increasingly more difficult levels to clear. All you need to move on to the next level is to catch enough bubbles. How many you need to catch is determined by how many total bubbles there are for that level. The number of bubbles caught is tallied in the top left corner along with the total for that level. Once your score turns yellow, you have caught enough to advance. Catching more than you need will award you a bonus score. And if you catch all of the bubbles for a level, a special bonus fruit will appear for you to catch during the following level. The backgrounds and music change about every 3 levels, which adds to the overall balance of the game.
Again, this is not a very deep or complex game by any means, and you may even think I'm a little nuts for mentioning it. However, there is definitely some enjoyment to be found in this simple yet well-executed game that I just had to share.