This is one of the few books in the history of literature that generated an entirely new genre (interactive novels / gamebooks): you can't miss it!
It is true that there are previous books that used similar concepts, but none of them made it as widespread and popular as this: that's why it can be said that this book generated the new genre.
The book itself is sometimes a bit naive (normal, as it's the first of a new genre...) but definitely entertaining, good re-playability and a paragon set for all future interactive novels: a door open on a new world!
This particular reprint is part of a more recent revamp / relaunch of the serie and the genre and perhaps some naivety becomes retrospectively more visible (now that there are plenty of books of this kind, that can build on the experience of the Warlock of Firetop Mountain. Nevertheless, this book is very valuable and enlightening.
Compared with Puffin original edition, this Wizard reprint is slightly bigger and with bigger fonts: I quite appreciated this change.