"What is the true nature of self?" is a very big question. Some may argue that it is the biggest question, and there is no definite answer, while others swear by religion as an explanation for our being. Whatever your answer is, it will be challenged in The Talos Principle. On the surface, The Talos Principle is a very beautiful (and very challenging) puzzle game in the vein of Portal, whose puzzles are very satisfying to solve (addendum: you don't have to solve the puzzles in order, you can jump between levels, and in most of the game, worlds.)
In my opinion, one of the highlights of the game is the interaction with an AI known as "Milton Library Assistant", who communicates on Tandy-style computer terminals found in many locations throughout the game. (The terminals are mainly used for collecting files that supply you with world building, à la Resident Evil). Milton Library Assistant is a very interesting character, as his views change depending on your own personal philosophy (or at least the one you insist is your own). This leads to many colorful discussions and debate, and may change your personal worldview, as it did mine. Such a feat is something which is something that I never expected a puzzle game to accomplish.
Short disclaimer: While I play many puzzle games, I am by no means good at them.
The difficulty in this game is, to put it mildly, brutal. I easily sank 24 hours into this game during my first playthrough. One of the last puzzles alone had me stuck for a good 3 hours. The puzzles are in no way unentertaining, though. There are over 120 puzzles in this game, and having played through all of them, I can say that I loved every single one. There is nary a one that made me think that they were padding the game out. All of them felt very fresh and very natural, with almost always complex solutions to seemingly simple problems.
In conclusion: this game is fucking fantastic, through and through. Not only is it one of the best games of 2014, it's one of the best games that I have ever played.