Despite a rough start, I certainly think that this book is better than its predecessor. There's a much more solid plot this time: the end of the world is coming and if Rincewind can't get to a certain place soon enough, there's nothing that can be done to stop it. Unfortunately, he's pretty much stranded and very far away from where he needs to be. This apocalyptic theme gives a sense of doom and darkness to the whole novel and I think this works as a good contrast to all the silly characters and events that we get to see. I like all this a lot more than the seemingly pointless wandering of the first. I have to say that there’s also a lot of genuine emotion this time and I did actually find the ending of the book to be rather sad.
Much like last time, Twoflower and his Luggage are a good source of humour and I like the dynamic between Twoflower and Rincewind. One character who is significantly expanded on this time is Death. Here the protagonists visit his home and get to meet his adopted daughter Ysabell in what has to be one of the strangest, but most interesting sequences I've ever read. There was also an multi-dimensional shopkeeper who I especially liked because I just kept thinking "Wouldn't it be really lovely if things like that were real?"
On the whole, if you liked the first, you'll definitely like the second and if you didn't like the first that much, but want to get into Discworld, there's more chance you'll like the second because it's better. I think the main difference is that this sequel is a lot more structured and seems to take itself more seriously too and that can only be a good thing.