No puzzle was uncrackable however and after revisiting hard ones over a few days I was able to solve them all. When you do finally solve a puzzle it is very satisfying and a real sense of accomplishment.
While I appreciated the visual art of the game immediately, I was too focused on the puzzles to truly appreciate what I was experiencing during most of my play-through. Only after finishing the last sequences and looking back on the game did I realize just how brilliant the game was. This is as much a work of philosophy or art as it is a video game. A true masterpiece.