Back to the early Discworld, and the style is very different to late Pratchett, and still more like The Colour of Magic than Guards! Guards! (its direct predecessor). Maybe that's just a Rincewind novel thing; they were never my favourites.
If memory serves, this originally started off as a big, Kirby-illustrated book, but I've got the pictureless paperback. It's short, at 155 pages, and rather more like a stretched-out short story than a compressed novel. The usual Discworld plot arc is not present.
To be honest, it's surprisingly bleak (maybe Rincewind's world-view?). The book covers all of time and space for the Discworld, with the overwhelming theme of people being a bit rubbish and never improving. It's a bit of a contrast to the "in the gutter, looking at the stars" ideology of so many of his other books.
In many ways, the feeling of the book is surprisingly Douglas Adams, from the creation of the universe to its ultimate entropic death, all life evolving from an inattentive time traveller, fallible creators and more. Maybe a bit of throwback to Strata too.
The humour is Pratchett, but somewhat hit and miss at the early end of the series. A few too many "whore" homophone jokes. A tribe that invented wheels but... not using them as wheels? The idea of a "demonology hacker" is fun, but never goes anywhere beyond Rincewind having a rather cardboard cutout early in tow.
In other places, jokes of the slightest subtlety are then explained. Apparently he doesn't have the confidence yet to keep throwing jokes at the reader, and let them just catch what they catch.
Having said that, There are still sly little references that I'm pretty sure I wouldn't have got on the last read-through, like the "It can get so very lonely, when you're twenty million light-years from home." Rolling Stones quote. I always wonder how many others I miss. The universe popping into existence with a little musical twang feels very much like a microcomputer boot-up reference, although perhaps a little early in 1990.
Is this book any good? Not really. It's short, it got me through half a day in hospital. I can't complain too much.