Agreed, it was such a cool documentary. I watched it on a flight back home from NY over the summer and would love to see a follow-up someday (although I doubt that will happen).
It was wild seeing how involved some of them were in the music scene prior to Zep forming. I knew Page was pretty active but didn't realize how much John Paul Jones toured around prior to the group forming as well. I also knew that Zeppelin 1 was pretty heavily influenced by American blues stuff (and some might say ripped from), but it's crazy that they essentially just formed a jam/blues cover band and recorded Zeppelin 1 around that.