I remember playing this game. I have it actually. Sadly my good computer needed to get fixed and i did that. Now waiting for an OS.
Easily one of my favourite puzzle games ever: fascinating, beautiful, intriguing, and deeply thought-provoking. The thing I most like about it is that I've been able to solve the enormous majority of the puzzles by myself. I usually have to check the Internet for help at least a few times for most puzzle games. Once so far for TTP, and I've completed the main goal and am currently solving secret puzzles and such.
It reminded me of portal and crossword puzzles i did as a kid. Trying to think of another game that had puzzles back in the day. Zork? umm Half Life Two did that as well. Many games have puzzles but not in the way this one did. Sadly i never got the fourth but i did like the graphics and art with this notion that artificial beings can become human by learned how. I dunno its been a while since i played that game.