As a GM I've always been on the lookout for "Role Master" friendly material.
I was talking to my GM friend and business partner the other day and realized my definition of "RM Friendly" and his did not quite match, and where it did match the priorities were different. I placed "Distinctive Maps" as my #1 followed by "NPCs with clear motivations".
For the GMs out there, what game mastery attributes to a module do you look for or wish there was more of in the products you buy?