In a memoir, I expect that the events in the books have some basis in reality and aren't just made up completely. The events could be a pastiche of other events and may even have been massaged for better dramatic and comedic timing but will have some basis in truth. In many ways, I expect a memoir to read like a novel and to be emotionally, if not completely factually, true.
These memoirs are very well-written and do read like very good novels. There's something about the way that Burroughs writes that I really like. He describes events in a self-deprecating and yet deeply truthful way. He never really comes and and says what he's feeling: he never says that he's ashamed or sad or grieving or scared. Instead, the reader infers how he feels based on the event itself and the words he uses.
In this way, the reader becomes emotionally invested in the events that occur and really feels what the writer is feeling. I've been in similar situations as Burroughs and I found that I could really relate to those events. Reading those events actually brought up some past memories of mine... memories that I don't like to examine all that often. Examining them in the light of these books made them less terrible and more bearable and that made these books very powerful for me.
The family portrayed in Running with Scissors felt that they were inaccurately portrayed and they sued the author for defamation even though names and identifying details were changed. The family wasn't informed that this memoir was going to be published and were shocked at what was there. I can't imagine that most authors would necessarily get permission from the people in their books but I do think they should notify those people about the project before publishing. The case was settled out of court and on subsequent memoirs of his it's made clear that details and events might be changed.
Even though Burroughs didn't lose the case, the fact that he didn't contact the family before publishing the first book is very much in keeping with type of person the author is... he's selfish, vain, and shallow. He's a jerk. Oddly enough, even though he's a jerk, I still enjoy his writing. Maybe it's because he doesn't try to pretend he's someone else: he is who he is. I like that. I don't think I'd like him as a person, but I do like his writing style and his books and I plan on reading more of them soon.
Both Running with Scissors and Dry are quirky, interesting, funny, and easy to read. They're worth reading if you're interested in unusual families (Running with Scissors) or what it's like to get sober (Dry).