I enjoyed You Just Don't Understand: Women and Men in Conversation and know of Tannen's other books, so was interested to see that she has sliced her studies of conversation yet another way here -- along sisterly lines in You Were Always Mom's Favorite!
It's an interesting slice since, as Tannen writes, "A sister is like yourself in a different movie, a movie that stars you in a different life." She posits that these lives revolve around a subset of sibling rivalry where sisters connect and compete in attempts to align themselves for parental love. She supports that not through strictly scientific data but rather social anecdotes -- examples pulled from literature, pop culture, and her own interviews. It's notable that I've recently read two other books that incorporate "everyman" quotes; they were clumsy in insertion and vacuous in content and frankly spoiled the works. But here, Tannen knows expertly when to summarize someone's comments, and when instead to roll seamlessly into a spot-on and memorable quote.
A couple quibbles. First, contrary to the subtitle, this book is not much about conversation. Rather, it's primarily about psychology and exploring the underlying family roles and dynamics that sometimes bubble up into verbal and nonverbal communications.
Second, Tannen leaves no stone unturned, no shade of gray unexamined. At one point, she refers to the 17 single-spaced pages of research notes she'd accumulated for one topic; I think she included every one of them in this book -- first via a complete, fully formed example, then appended with a summarizing paragraph. The wordiness and repetition grew tedious, and tolerable in doses of at most a chapter at a time. I actually think an audio version would be a better fit for Tannen's smooth, conversational (!) style, and would make any repetition feel reinforcing rather than frustrating.