I just played THE 7TH GUEST for the first time last week and had a great time with it. (Love those creepy cursors but not those spiders!)
After finishing the grate puzzle fairly quickly, I stepped into the maze without realizing what I was getting into and before I saw the map on the rug upstairs. I got so lost that I finally had to quit and reload to check out the map. However, I also had to redo the grate puzzle which, for some reason, was much harder the second time around. (Probably because it was nearly 1:00 A.M. and my cognitive powers had already gone to sleep.) Anyhow, I made it through the maze only to be rewarded with...another puzzle! (Sheesh!)
Several people have said how difficult they thought the microscope puzzle was, but I was lucky to solve it after 3 tries. I thought the knight puzzle was a real buster, though.