How Amazing the Hackmaster 4th Edition GameMaster Guide is.
The reason I didn't know is because, as I mentioned above I never GMed. Unlike D&D where we all had a copy of all 3 books (much to my chagrin) the GM forbade us to bring or even own a copy of the GMG of any of the HoBs (Hackolepdia of Beasts). That was one of the few decisions I can say I was really in line with for that campaign. By ensuring that none of us had access to those books it really helped maintain and air of mystery about the game, something I really enjoyed. But years removed from the game I happen to stumble on my copy of the GMG that I had purchased when Kenzerco ran their bundle deals and decided to give it a look. I was very glad I did.
The GMG has so much information packed into it that I couldn't help but be blown away. This is a book I think I'll keep on hand any time I am running a game, regardless of the system. Aside from mining info from their HM4 specific rules like spells and training, there are numerous charts such as their expansive critical hit and critical miss tables to be taken advantage of. On top of that already valuable information they have generic information about everything ranging from Horses, to forms of government, to types of punishment used in medieval societies. The treasure chapter goes outside the confines of HM4 and talks generally of currency, taxes, and types of merchants. I think my favorite might be chapter 10: GameMaster Procedures. This chapter deals generally with being a GM and all the pitfalls and difficulties one might face from record keeping to arguments and complaints.
Because their deal with WoTC expired Kenzerco can no longer sell the vast majority of their 4th edition material. However, you can still purchase the GMG and other Hackmaster products through Amazon vendors. Prices at the moment start at $13.08 used and $34.90 new. I recommend GMs of all systems pick up a copy, there is great information for everyone in there.