This is a documentary mainly aimed at the casual fan, and trying to condense 75 years into three hours is always going leave holes. Let's start with the good stuff.
Liev Schreiber is a great host and narrator. He sets the tone well. Not all actors are good narrators, but Schreiber delivers.
The interviews are an excellent cross-section of folks from across the years. In this time where superheroes dominate the culture, it's eye-opening to remember the humble beginnings.
The odd stuff:
For a film that seems to want to be an overview for the masses, it does dive deep into the weeds at times, notably with an extended focus on 1986, and the one-two punch of Dark Knight and Watchmen. Yes, those are two utterly pivotal books, but I'm not sure they require as much screen time as they were given. This also leads to one of the omissions: We should at least have a passing mention of Camelot 3000, the 1982-1985 DC maxi series that paved the way for the direct market. Since the documentary spends time talking about the collecting bubble of the '90s, it's surprising to leave out this book.
The omissions:
In addition to ignoring the direct market, there is no mention made of the black-and-white indie explosion of the '80s. I think there is one brief glimpse of an Eastman/Laird TMNT cover. Not a mention of Dark Horse comics. In fact, the only modern company mentioned outside of DC and Marvel is Image.
While some mention is made of Black Panther and Luke Cage in the 70s, not mentioning Milestone seems odd. After all, Static Shock brought that universe into the mainstream, and that's kind of the point of the series: comics gone mainstream.
I could go on, but every documentarian has to make choices. Suffice to say this: what's on the screen is superbly done. But there's more to tell. Hey, Ken Burns! I've got an idea for you...