I\'m trying to make (figure out how to..) a 2d platformer in XNA.
I know how to create a tile grid and how to perform collision detection. I perform collision detection
You probably need a bit more than collision detection for a game like Braid. I would assume that you also need a physics engine. I would recommend that you take a look at Farseer Physics engine, which is 2D engine that works very well with XNA. It supports a number of different techniques for collision detection.