According to Cain

I like a lot of the ideas in this game, and many of the puzzles were solid, but I became totally dependent on the in-game HINTS command, and I felt I had to conclude that a lot of the puzzles weren't fair.

(Spoiler - click to show)A number of the puzzles (including three of the compound spells) require you to LOOK UP X in the book where X is a term you haven't seen mentioned in the game yet. That could be OK if the answers were extremely clearly right in hindsight, but I kept finding that I tried a bunch of reasonable LOOK UP X commands, and then I'd check the hints, and then… womp womp, none of my reasonable guesses worked. Instead I should have looked up Y.

I don't think it makes sense to have "guess the topic" puzzles unless the author provides support for a lot of topics (or, at the very least, a lot of synonyms), and at the minimum help me out with "warmer/colder" hints. Otherwise, after a few failed guesses, I'm forced to assume that there's no puzzle to solve here at all. Good puzzles have to seem inevitable in hindsight, and none of the "make a wild guess about what to look up" puzzles ever did.

In addition, the puzzle in the cavern was… not good. I'd put the obsidian slab in the obsidian block, and didn't realize that I could bring it back out again. But even if I'd brought the slab with me, I put a bone on the altar and it didn't seem to do anything, so I never discovered that the bone would disappear.