Disowned Adaptation: Tommy Wiseau wasn't a fan of the book. It has been speculated his disdain stems from the sections about his life before he came to San Francisco — the book itself notes that the topic is something of a Berserk Button for him. The movie, on the other hand...
Life Imitates Art: After finishing his scenes, Dan asked Tommy to repay him for his boots, which were damaged during the rooftop fight. Dan essentially had to intimidate Tommy into reimbursing him, to the point where you can't help but imagine him going "Where's my fucking MONEY, Tommy!?!?!", just like he went "Where's my fucking MONEY, Denny!?!?!" in the film.
Missing Episode: Most of the movies and TV shows Greg talked about being on before The Room. You can't find his car commercial online, the only online copies of the episode of Nash Bridges he was on are from a syndicated rerun that seems to have cut his scene out, and you can't find the episode of Days of Our Lives he was on. Plus the Deleted Scenes for Metro aren't on the DVD so you'll have no luck finding the scene he was in that they cut out of the movie. The only pre-Room things of his you can find are appearances in Gattaca, Patch Adams, EdTV, and Retro Puppet Master.
Actor Allusion: On the podcast How Did This Get Made?, June Diane Raphael has a reputation for proposing off-the-wall questions and theories. In The Disaster Artist, her character Robyn Paris is the one to theorize what The Room is actually about.
James Franco required substantial makeup to approximate Tommy Wiseau's distinctive appearance.
Greg Sestero at 6'2" towers over 5'7" Dave Franco, who was cast to play him in the film. James's reason for casting his younger brother was because he interpreted Tommy and Greg's relationship as being fraternal and was hoping to match that interpretation.
Dan Janjigian (the actor who played Chris-R) is a 6'2" Armenian man. Zac Efron is a 5'8" Jew. He makes it work.
Tommy Wiseau approved of both Franco brothers' casting, although his personal preference for himself would have been Johnny Depp. He later gave the film an absolutely glowing review, saying a lighting issue in the first scene was the only problem he had. James Franco pointed out to Wiseau that he had been wearing sunglasses when he saw the movie.
Juliette Danielle was perfectly happy with Ari Graynor's performance as her.
Billing Displacement: Though James and Dave Franco are co-leads in the film, with the film almost always following Greg, James Franco as Tommy Wiseau is the main draw of the film and is usually billed first in promotional materials. However, in the end credits of the film proper, Dave is billed first. Furthermore, while James was submitted and won in the lead categories in the awards circuit, Dave was submitted as supporting. Ironically, James had pushed for Dave to be billed first and submitted as lead so his younger brother could get more exposure.
Channel Hop: While the film was produced by New Line Cinema, the US distribution rights were sold to acclaimed indie distributor A24 after New Line parent Warner Bros. cast doubt over its commercial potential. Warner Bros. still retains the rights for most international territories, and their logo still appears on the US version.
Creator Backlash: Sandy Schklair is apprehensive about Seth Rogen's portrayal of him, especially since Rogen turned down an offer to meet up with Schklair and talk about the role.
In-universe, Philip ("Denny") comments on it being odd that he's playing a character over ten years younger than him, which Greg visibly agrees is strange. Dave Franco, who plays Greg (who is nineteen when the story starts), was over thirty at the time of filming. Like the actor he's portraying, however, he's baby-faced enough to make it work, not to mention the film covers a period of about 5 years.
The film also cast 33-year-old Ari Graynor as Juliette Danielle, who was 22 when the film was being made. And June Diane Raphael (36) as Robyn Paris, who was in her early 20s, mid-20s tops, during the making of The Room.
Fandom Nod: For the longest time, Chris R's scenes have been acknowledged by the fandom as being the best performance in The Room. It even reached in-joke status of his actor being an actual drug dealer who just wandered on set. Disaster Artist plays with the idea by having him instead be a Method Actor who got a little tooin character. (note that according to the book, this portrayal of Janjigian is 100% accurate)
Method Acting: James Franco maitained Wiseau's accent throughout the shoot. This sometimes made it unclear to the production crew whether his directions were meant to be applied to The Disaster Artist as James or part of the scene when shooting The Room as Tommy.