I agree with most previous comments: it was not obvious I could click on the book. Mainly because it looks similar to the compass that is not clickable. So the first time around I died before I understood all the rules (and read the comments ;)
Another little thing, perhaps the needle could wriggle when an enemy is close? I had te remember to look at it when no enemy seemed in sight. Just having it appear didn't catch my eye.
I stopped playing when I was stuck: there was a golden key, but two golden doors. I guess I opened the wrong one… I could see the exit with the eye, but no way to open the door!
Apart from these niggles, it plays very well!