Adventure games are tough to get right: they generally rely on the craftiness of their puzzles and the strength of their story, and balance is key. Hard puzzles are fine, as long as they involve some sort of logic. I don't appreciate the kind of adventure game that has you put masking tape over a mouse hole so it picks up the hair off the mouse, allowing you to use the hair and some glue to make a fake mustache to sneak into the library. What kind of sense does that make?! Who sneaks into a library? It's a public building!