I love this game so much but I have not played it since the 90s, so there is probably a heavy dose of nostalgia talking.
Regarding whether or not you need a walkthroug, I would say that it depends. I finished it without one at the time, but I am also a big fan of the Discworld books. If you are “tuned in” to the logic of the world and the humor etc., I think you start to understand the logic. Or lack thereof, depending on how you view it.
Is there a legal way to get this game nowadays? I would love to play it again.