Braid is fantastic and well worth playing. But I know it’s a busy time of semester. Some links if you didn’t have time to play it through (or if you are click-challenged like me and can’t get that far with it):
Opening: watch until you see the first screen with clouds and the narrative framing and then far enough in the gameplay to see the player use the shift key to rewind time to redo after making a mistake (just before 4 minutes). You can see more uses of the reversal of time if you go a bit further.
Conclusion: the hidden ending that you only see if you collect all the stars in the game.
And if you have time and the inclination:
Super fast playthrough – 24 minutes (thanks, Matt!). You can see how the temporal element becomes used at points in how the player overcomes obstacles.