It was rather entertaining, even a bit spoilerish about the show's path if it had continued. Like what was said before, not everyone was there. Joss only was seen at the Con itself and Ron Glass made no appearance at all, which was somewhat disappointing. There were others who had done their interviews separately, I imagine they were off doing other things and didn't have time to make an appearance. If you're a fan of the show, it's well worth watching.
The narrator sounded a lot like Ron Glass. I, too, really enjoyed the documentary - truly a shame it will probably never come back.