So I saw The Disaster Artist. Not a bad little film -- but if you haven't seen The Room (the movie whose making TDA depicts) yet and plan to watch both movies, I'd recommend starting with TDA. Basically, TDA can't answer its most intriguing questions, so what you're left with is the reveal that these guys made a terrible, terrible movie -- and one who's already seen The Room knows that all too well. Viewed in the reverse order, however, I imagine TDA could heighten one's anticipation of Tommy Wiseau's cinematic abomination.
If you've already seen The Room -- and you were so fascinated that you need to know just how it came into being, including the origin of certain character behaviors and the context for certain takes -- TDA will totally be your jam. For me, it ended up feeling kinda superfluous: like the Star Wars prequels, albeit more competently executed.
Bonus for fans of Nathan For You: Nathan Fielder has a small part in it.