One is that the film never really explains why people consider Moog's synthesizers to be "better" than any of the others. Even if you just focus on "classic analog synthesizers", the competition is pretty stiff - the Arp 2600, Yamaha CS-80, Sequential Circuits Prophet-5, for example. If they'd even had a few musicians talking about "that Moog sound" or the panel layout or something it might have been enough.
The film doesn't explain why Moog's designs beat out other, more radical/interesting concepts by contemporaries like Don Buchla. It doesn't explain why Moog's instruments have endured to be classics like Fender guitars. (In fact, a lot of those vintage instruments' value comes from the "Moog" name alone.)
Another is the general shapelessness of the film. Bob Moog's life story so far has a very powerful dramatic arc: Young genius starts making Theremins, wows music world with breakthrough synthesizer "modules", rockets to success, is bad at business, makes some mediocre/bad/disappointing products, loses control of company and name, lies low, starts new company, re-buys rights to name and makes "triumphant return" making basically the same instrument he succeeded with decades ago.
Instead, we get a bunch of rambling interviews with a few folks, many of whom are far from key players in the Moog story. For example, the inane commentary of Money Mark, who doesn't even pronounce "Moog" correctly (in case you're wondering, it rhymes with "ROGUE").
In particular, the lack of inclusion of Wendy Carlos (who would be a good documentary subject as well!) is absolutely unforgivable. Other noteworthy folks such as Tomita and Jean-Michel Jarre are conspicuously absent.
Moog himself has frequently said he wants to make instruments that are warm and expressive. Yet most of the music heard in the film is exactly the sort of "blippity-bloop" cliché that turns most people off to synthesizer music in the first place. None of it approaches the power of Clara Rockmore's Theremin performance in the "Theremin" movie.
So what does it do right? Well, it tells you that Bob Moog is a really nice guy - the sort of person you wish you were related to so you could see him at family gatherings. And it had one or two very entertaining Moog-related stories. That's about it. I am willing to cut the filmmakers a bit of slack for some things - it was a "low-budget" independent film, after all.
But the more I think about it, the more disappointed I am. This is inevitably going to be considered the "definitive" Moog movie, and that's a shame. My advice would be to go and rent "Theremin: An Electronic Odyssey" instead. It's much better all around.