David is a game, an arcade game, and David is a very unusual game. Our little polygon hero finds himself in a world of abstract shapes and giant evil beasts that are out to eviscerate him one angle at a time. His only powers are the ability to run away like a little yellow belly and fire slingshot-like blasts at his foes. Sometimes he feels powerful, sometimes victorious, but there's always nagging feelings of helplessness and hopelessness in this dangerous world that just wants David to go away.
Cube & Star: An Arbitrary Love is the kind of game you fire up when you know you want to play something but aren't quite sure what you're in the mood for. The delightfully abstract experience from Doppler Interactive puts you in a gray world and says "now go out and do stuff". That "stuff" involves bumping into trees, painting the ground different colors, knocking corners with other shapes, collecting some of the many strange items hidden throughout the environment, and just generally rolling around to see what you can see. Somehow, it's bizarrely entertaining.
Starseed Pilgrim is a very, very unusual game. Created by droqen, author of Probability 0, it's best described as an abstract puzzle game with some light musical elements and a touch of sandbox-style gameplay. That doesn't do the experience justice, though, as its real value comes from the sense of exploration and wonder you'll get trying to figure out which seeds grow which blocks and what exactly you're trying to accomplish in this bleak world.
Proteus is a exploration-based piece of interactive art by Ed Key and David Kanaga. In it, players take a walk through an abstract procedurally-developed island. While Proteus is probably not going to challenge the conception some have of art games as low-rez inaction-fests, that niche of gamers who'd be interested in a chill 45-minute retro vacation will find it a place worth hearing, and a song worth exploring.