With my general time constraints on playing games, I'm probably the last person who pre-ordered it to finish, but I finally did. I thought the game was enjoyable, not as tense as the first one. Most of the tension here was thinking, Nelson, you really ought to not be saying these things to this person you just met.
As someone in the U.S. with a pretty good math aptitude, the puzzles were mostly straight-forward. Some of them might be too advanced math-wise for younger players, though. There were a couple of puzzles I had to let run at least once to see how they really worked, because I didn't understand what the instructions were saying, but it was better than the first Puzzle Agent.
I wish there was a way to unlock the bonus puzzles without having to go through again and win everything on the first try. Like I have time for that.
Anyone want to post a spoiler thread with screen shots?