Finished Braid - somewhat hated how some puzzles require you to know some game physics (that I didn't know and took me forever to figure out how to do it), but if you want something to challenge your mind a bit beyond the typical "pushing the block" type puzzle game (with a bit of Mario mixed in), this is for you.  I think it might've been a bit better if it didn't require you to have all 60 puzzle pieces to finish the game.