It doesn't matter if you have 1001 days to waste your time. You won't be able to complete this game without going mad.
The good news about Discworld is that dialogue is pretty good, but you need the cd-version with voices to appreciate that.
Everything else is a complete disaster of epic proportions. You can't complete Discworld. It's just a fact. The things you need to do to advance are so ridiculously stupid and insane that you will have a hard time figuring out what to do. The main character, Rincewind, despite of having a funny voice, is utterly retarded in the sense that his descriptions about items and stuff and his dialogues with characters in the game are 100% improductive. The dialogue is stupid and funny, but gives you ZERO clues about what to do next.
And as I said, "what to do next" could be as retarded as "using a butterfly on a rope to get a dish of fried chicken so you can then use it on a black hole that will erupt and will make a sandwich with french fries appear in your inventory".
Since you need to be drunk or crazy to be able to advance, you may take the logical resolution of browsing/getting a walkthrough guide on gamefaqs. Of course, looking in a guide kills the fun and the proud of saying "I completed the game without using a guide".
Seriously, there is NO sense in this game. I DON'T CARE if the books are great, this should be a good game for anybody who likes to play adventure games, but the truth is that it is a horrible experience.
Since the minimal score you can give in GS is 1, I will give it a 1 and will put the excuse that the dialogues are funny.
Cheers!