The greatest brainstorming document of all time.

[Hexed Pressman]

...any prep the GM ~gets to~ do is prep the GM must do. And increasingly I find that if I'm going to prep, I want to prep my own work, not somebody else's. If I'm going to run something out of a book, I want that book to do my work for me. Cracking open a new RPG book that seems to expect me to do hours and hours of prep just to get the game to the table (like Mythic Bastionland, or Veins, or any of the others) feels like I'm buying myself homework.

I think that, for myself, that work is part of the GMing experience that I enjoy. I look forward to building out worlds and settings to play in so I don't find these types of books a detriment to me.

...there's a level of specificity to some of these "toolkit" games that feels like it undermines itself -- how much of my own creativity am I really going to inject into a Mythic Bastionland sandbox?

That's an interesting point. I guess though that if you're buying into Vaarn or MB that you want to run a Vaarn or MB-like setting. I run my own settings pretty much 100% of the time so these books end up being toolkits that I borrow from more than something I would run in total unless I was running it to specifically explore the book/system.