Tobiah Q. Panshin's The Game Master is an interesting book from front to back, one which is both wonderful and cringe-worthy at the same time. Of all things, perhaps its worst is its inconsistency; verging from academic-styled formal writing to wonderfully light informal prose, it does few things explicitly wrong but doesn't seem to know where it is. Nonetheless, it's something that I would recommend, with a caveat.
The Game Master, for instance, is aimed at novices, and while it's not terribly difficult to read and does a decent job at explaining its terminology (sometimes after using it nonchalantly), it has some things that are both not terribly applicable to a new player or GM, and can potentially cause more harm than good. While it's generally thoughtful, there are several instances of hyperbole (for instance, the statement that a freshly created vampire in Vampire: the Masquerade can shrug off machine gun fire) and it tends to do an odd mix of advanced theoretical work and some really weak practical examples.
Perhaps my favorite part of the whole book is its dissertations on narrative; while not a focus of the piece it has some things that would have helped many of the novice GM's I know incredibly. Is it the best source for this? I'm not entirely sure. The book does a good job of discussing the role of group narrative but often leaves bits and pieces that I'd like to see out, something that doesn't do too much harm to the general point of the book as an introduction to gaming but hinders it in its value. Still, the sections on narrative are well-made and I'd recommend them to anyone either as a refresher or an eye-opener. Unfortunately, some of the more game-related things do not fall into the category of being so wholly beneficial. While it's clear that Tobiah has a great understanding of roleplaying as a hobby and a great conceptualization of various games within the context of the whole canon of gaming, the writing within has the unfortunate effect of transferring very little of it to the reader. There are footnotes that are assertively unhelpful (one, for instance, points out the meaning of the term "min-max" the page after a prior footnote uses it), and a lot of blanket assessments that are just not accurate, though they may be true in a handful of cases. The actual game advice is much less helpful than the deconstruction of narrative forms that create a satisfying table experience. A lot of this may be my own personal opinion, of course, since as Panshin recognizes much of gaming revolves around having fun, and different people will have different definitions and sources of fun.
All-in-all, The Game Master is not a conclusive resource for advice on running a game, nor is it the first thing I'd hand a prospective player or game master and tell them to read through it and gain some sort of inviolate knowledge of gaming. Of course, such a thing will probably never be written-such is the nuanced nature of gaming. I'd place it in the mid-range; something for someone who's run a few games and formed their own opinions on how things work, or who already has a basic knowledge of how things work-it's a wonderful contribution to the theory of gaming and play but not necessarily a solution to the ills of a novice.
It's available on a pay-what-you-want basis, and despite my harsh criticisms and the general fluctuating quality, I'd give The Game Master a 4/5, and actually recommend that anyone reads it, at least a little, because there are valuable perspectives to be had here.