Let's not mince words: this is a very enjoyable book. Despite the seemingly dull premise (Wizards playing football? Are you mad?), the plot is entertaining and surprisingly deep, though the book starts out a little slowly and it takes thirty or forty pages to really get going. It's less about the football itself and more about the people
whose lives are affected by the game. Most of the focus is on new characters (my favourite of these being Nutt), but many Discworld regulars make an appearance as well.
Pterry's writing is also just as sharp as ever, utilizing his trademark sense of playfulness and love of wordplay. As always, any scenes involving the Unseen University staff will steal the show, particularly when the wizards argue. This installment notably has a few more running gags than the average Discworld story, but whether this is a good or bad thing really depends on your personal tolerance for that sort of thing (the first review on this site clearly doesn't think much of them). I found them funny, at any rate.
The best part about this volume, however, is the sheer amount of references to earlier Discworld stories within in. Pratchett normally isn't overly bothered with continuity, so all the little references become immensely satisfying for longtime Discworld fans, such as myself.
But the book is not perfect. I can't remember there being any truly laugh-out-loud moments in it, which is a shame. Granted, Pratchett's humour is usually more thought-provoking or small-chuckle-worthy than laugh-out-loud funny, but still, there's usually at least one such joke in all of his books, in my opinion, so the lack of one in this volume is certainly a drawback. Another thing is that the normally reserved and stoic Lord Vetinari is seen laughing a few times in this book. This is at odds with his previous characterization, which wouldn't bother me as much if he weren't my favourite character in all of fiction. That said, though, that is the only actual derailment that I have noticed with any of the characters in here, and it's a fairly minor one at that.
So, all in all, this is a good book, but certainly not Terry Pratchett's best. It shouldn't disappoint fans, unless they are expecting it to outdo the earlier volumes. Definitely worth reading.