GiantKiller

I was pleasantly surprised by this game. (I wasn't expecting much: a non-Infocom game from the 80s with an educational focus.) Yes, the parser is weak. Yet this was not a source of frustration: The game was clear enough on what you needed to do at each point that I had no "guess-the-verb" problems. It also comes with a player's guide that lists all verbs recognized by the game.

The puzzles are the game's main strength. Several are quite clever, getting into mathematical topics like tessellations, Eulerian paths, and prime numbers. I never felt like the puzzles were unfair - either for adults or for the intended audience of 8-14-year-olds. In fact, I could easily imagine a class of students bunched around a computer, saying "Try this!" and "What about that?", as they work through the game together.