We were talking about the merits of adventure games at work... Trace Memory came up for me because I played this a bit... but it didn't do a good enough job (for me) on setting the boundaries of where you had to go to find the answers to the puzzles... So this led to a discussion about game design and how you set limits in adventure/puzzle games but yet still give the gamer enough flexibility to feel like solving the problem is not easy.
I guess that is why game designers make the big bucks! :)