The "classic three" division that began with AD&D-- Player's Guide, Game Master's Guide, Monster Book-- has been taken as a sort of gospel by a number of other games (although certainly not all). I've explored this somewhat in an earlier post that focused on the player's guide. But now I'd like to turn my attention to the game master's guide.
Just what function does it serve?
As I indicated in my thoughts on the player's guide, I think that most of the actual rules of play belong there. After all, they are the players. And the players, it seems to me, need to know how to play. So that's where the rules for combat, and spells, and (obviously) character creation and the like need to be. The monster book is self-explanatory; it's something that could, in theory, be folded into a game master's book, but due to logistical reasons, there's a compelling argument to break it out.
To understand the role of the game master's book, on the other hand, requires a brief analysis of the game master's role. The game master is referee and interpreter of the rules, sure. But in an old-school type game, he is also the person who creates the adventure and the campaign in which it takes place. Newer versions of the game tend to rely on pre-published adventures and settings, simply because there's a relatively high amount of preparation time required to make sure the encounters are properly scaled, etc. (That is not intended as any sort of derogatory remark, I should add; it's simply a function of the more "even" approach to scenario design built into the new rules.)
There, I think, is where a game master's book can shine. There will, of necessity, be certain game-mechanics type material that isn't appropriate for the players to have everyday access to. (Although, as an aside, I think I can say with complete certainty that I have never used the "Detection of Invisibility Table" on p. 60 of the AD&D DMG; there seems to be a lot of "flyover country" in there, and that's a phenomenon I'd like to avoid, hopefully with better organization.) And a certain amount of Game Mastering 101 is probably needed, although in Emprise!™ it will probably find its way into the boxed set that is specifically aimed at beginners.
But I feel that the best use of the limited number of pages in a game master's book is practical tools to assist in the creation both of scenarios and campaign settings. There will be lists of magical items and treasures, to be sure. In fact, I'm putting together an entire section just on non-magical treasure; it'll be a (hopefully) quick and easy way to put together treasure troves that are much more interesting than simply "a chest with 5,000 g.p. inside". And I think the potential of treasure maps has been long overlooked.
But also a running commentary on some of the implications built into that player's guide, and how they impact the decisions the game master must make. For example, the description of the thief class takes for granted the existence of a thieves' guild or similar organization. How does the game master handle such a thing? What are the consequences of not having one? The same applies to most of the classes, and the races also have their own setting-impacting assumptions that must be dealt with. What will happen to a campaign that allows drow, deep gnomes, and gray dwarves? What happens to a campaign that doesn't allow them?
on the order of the Temple of the Eye from Hall of the Fire Giant King, and you'll understand what I'm thinking about) and ample commentary on the design of such things. Give some examples, give some advice, and push 'em into the lake. THAT's how I want to approach the vast majority of campaign design in this book.
On the level of the individual adventure, the toolbox concept will once again come into play. Sure, there will be advice on basic dungeon design, theory on sandboxes and megadungeons and and set-piece encounters and the use of plot. Again and again and again chock full of advice on how the choices the game master makes early on might have an impact down the line.
But I'm also a big fan of things that are immediately practical. I'm not sure about a random dungeon generator (those things are never quite as neat and useful in reality as they seem to be on paper), but certainly some random tables are in order to help with certain design elements; being able to design memorable (but hopefully not cardboard) NPCs on the fly, for example. Traps and tricks. Stand-out dungeon design elements; quick ways of working up details for shrines, statues, bottomless chasms, humanoid lairs, and so forth. More than "mere" dungeon dressing... well, yeah, I'm a big fan of that kind of stuff (and I love dungeon dressing too).
So, anyway, that's where my mind is currently on the subject of the game masters guide, it's function and contents. Now, back to work with me on this rainy and windy Saturday afternoon (we've already had one tree go down, which missed the house by about five feet, I might add).