Even though the game itself only takes about 7 hours total to complete, it took me months to finish. I'd play it for a while, get stuck on a tricky puzzle, and ignore it for a few weeks. Eventually, I'd go back with a fresh head and clear the puzzle only to get stuck at another point. I'm glad I wound up playing it that way, as I think I was able to appreciate it a little more than I would have had I blown through it in an afternoon. Amazing game, and I can't wait for SotC.
Also, when you beat it, make sure you watch past the credits.