This is a fantastic sandbox FRPG environment. There is enough of a skeleton there to get you started and enough left open to expand in your own way. I have not had this much fun with an RPG in years. My players are Really digging it.
The RPG mechanics and Old School D&D compatible and very unobtrusive to the product as a whole. This is 99% source material with a few stats thrown here and there to give you a rough Idea of an NPCs relative power level. If you are Familiar with Basic D&D, AD&D or a retro-clone, you will have no problem running this in any FRPG game you like.