The Black Forest:
The title is pretty apt. You start the game wandering around in the darkness, a little black square (with cute little white eyes) against a black background, in a maze with black walls. You only know where the walls are by bumping into them. Eventually, though, you find a friend: a little pink square that follows you along and paints the ground behind itself, letting you see where you've been. It's with the help of the friends that you'll be able to find your way to the exit of the maze, because they'll be painting your path so that you don't double back.
The game is effective because it manages to, in a couple of deft and simple strokes, give you a pretty powerful emotional experience. The early part of the game, where you're alone and pretty much navigating blindly, is frustrating and lonely. As soon as you touch your first friend, though, you add both color and music to your experience, and with each friend you touch, you get another gorgeous layer to the music and another helpful little buddy illuminating your path. You can find the end without finding all the friends, but by the time you're there, you'll feel so bad about leaving the little guys in the dark that you'll go off to save them anyway. As a bonus, while the last friend you touched follows you faithfully, the other friends roam around their areas at random, with the benefit that sometimes they illuminate paths you hadn't seen before. After all, isn't that what friends are for?