As others have said in more eloquent reviews, I think this is a decent game that I cannot recommend to anyone aside from the most die-hard fans of puzzle games, i.e. people who are happy to solve puzzles for the sake of solving puzzles and nothing more. My thoughts on the game align perfectly with Joseph Anderson's, so I would highly suggest you watch his review if you are considering playing this game. You can listen to it instead to avoid puzzle spoilers. Having the endings of the game spoiled makes no difference since none of the endings are worth the time it takes to play through the whole thing.

For my first couple of play sessions, I ended up cheating and just looking up the answers to puzzles whenever I got confused or tired of them after a while. My third and final play session with this game resulted in me defaulting to looking at guides before even trying to solve the puzzles on my own. Obviously this is mainly my fault as an impatient player, but I have played through many other 3D puzzle games (Portal, Talos Principle, etc.) in which I felt shameful for looking at online guides, and did so sparingly. With The Witness, I felt nothing.

To sum up my thoughts: I feel like this game has glimmers of brilliance, but overall is just a giant missed opportunity.