This book of Terry Pratchett has received mixed reviews, some praise it as the best of the Discworld series, some say it's the worst. Personally I am one of those who didn't like it, but that's okay. It had its funny moments, but if your not a fan of the main character of an individual Discworld book, you won't enjoy the book so much. In other words, if you like Rincewind, you will love this book too and will want to reread the whole series of his books so that everything stays in context. if you don't like the false Wizard's stories so much, I'd put of reading this book until there are no more Pratchett books left to read.
For readers new to the world of Discworld I have to say this an ideal starting point in the series, just bear in mind that if you don't like it do not give up on the series until you've read at least one other book of the author with a different protagonist. Reading order is not that important so in choosing the first book to read pay attention to the back covers and buy the one which grabs your imagination the most.
One note on the American edition by HarperTorch: I bought this edition as it was half the price as the Corgi edition, but the Americanization has taken away from the genuineness of the book. I don't have anything against American spelling, but it is my opinion that a publisher should respect the spelling of the author unless it creates difficulties in understanding, and even than the fact that changes have been made should be noted.