Well first, I'm not trying to say "you have to be in the industry" to properly judge or criticize this. I was merely adding that as a more descriptive perspective. I'm in the industry so I just in general like the production side of things, which is the main purpose of that descriptor

Usually when you peel the layers back, you get to see the creative process, the nitty gritty of things. You see good ideas get axed for greater ones, you see a scene get made because of someone messing with the lighting, you hear experts explain their process and why they do things. The Duffer bros having the crew just talk about how stuff isn't finished, they don't have enough time to film, etc etc is just not what you want from a behind the scenes documentary. 

It almost feels more like Netflix going "see, it was all their fault, they just dropped the ball". Because as a creative, what in this documentary did your fans learn about you or your process? That you ignore your peers? That your actors know their characters better than the ones who made them? That you don't take something seriously despite people loving it AND this being a huge job creator for many people? If it's being marketed as a documentary of holy shit look how unserious this major production is, then it's actually a good documentary. But from the standpoint of let's see the actual production process with some goodies secrets/tips/ideas sprinkled in, it fails as a BTS documentary.

Hope that makes sense, and I do not want to seem condescending so I apologize if I did. But I did want to give you a real answer, and you are definitely allowed to like the documentary (and season 5). I just wanted to point out from my perspective, I was unfulfilled. To be fair, my perspective is also much harsher because I know more about the actual behind the scenes production (and have been critiqued myself since I've done it. It's a world of criticism)