Goodman Games

Hello,
New to the system and wanting to get a real rulebook as I only have the quick start rules. My question is are all the rules books the same? Just cosmetic differences? Or does say, the 4th printing have updated rules or modules.

Thanks for your help!

- LCD

There have been some edits, the 4th printing has additional art, and the 4th printing has one new adventure (and does not have one old adventure) from earlier printings.

All printings are the same edition.