Braid is a clever, brain-straining puzzle game masterpiece. It's like playing Super Mario as Marty McFly.
You play as Tim, a generic, unexplained character. The controls are pretty straightforward, only you can rewind time with the simple use of the X button, and can change the speed of your rewinding with the left and right bumpers. This being a feature, death is not a factor in your making it through the game.
If you enjoy a difficult puzzle, give this game a shot. You'll definitely find your competence, skills, and patience put to the test.
After finishing the game, there is a timed mode you can play which is even more challenging for obvious reasons, and there are stars that are found in certain levels by going to great lengths. That being said, there is very little replay value in this game, as after finishing the game the first time you will probably feel accomplished enough and struggle building ambition for a second run-through.
All in all, Braid is a magnificent addition to the Xbox Live Arcade, and is a good title to have in your library, whoever you are.