Finally got around to play this game. I remember playing a pre-release version of the game and then abandoned it because I wasn't feeling it, but now I've completed it in its entirety, I can say that it's very, very clever, and the puzzles only get better and better.
I like the fact that rather than having one specific core mechanic and hook, this game has multiple unique and seemingly irrelevant mechanics at play. While you can argue that some of those are more 'core'-y than others, like the portals, all of the mechanics just work so well together that they feel equally important. I believe the game did a good job bringing all these ideas together and exploring them to their fullest potential.
All in all, great game, strongly recommended.