Great puzzles with flawless gradual building of skills. I never had to look outside of the game for help (The Witness comes to mind) nor use an in game hintsystem (none exists) a la The Room. The only ridiculous level design was level six in the Forgotten Shores DLC where I found it difficult to visualize a continuous plane in some circumstances where the character is walking upside down. But the solution was decipherable anyways so I didn't spend much time trying to convince my eyes to see something.
Story...can't say I paid much attention to it. I guess some "ancient beings" or something left the puzzles as monuments. Whatever. It is not crappy and stays out of the way.
I played the original game, DLC levels, and the Ida's Adventure standalone part.