One thing particularly remarkable about Amy Tan's writing is that she takes autobiographical accounts and turns them into fiction. We particularly see her accomplish this fantastic feat in her debut novel The Joy Luck Club; biographical elements she morphs into fiction include relationships between women in her family, her father's and brother's deaths due to brain tumors, and her grandmother's suicide (The Guardian, Hoggard, "Death as a Source of Life"). Thus one reason Tan's writing is so popular is because of how well she crafts her fiction while integrating autobiographical details.
She is also particularly reputed for writing about first-generation Chinese-American culture. Tan shows the struggles of the first-generation Chinese Americans of the 1970s, children of parents who were ostracized in the 1950s by their native land due to the rise of Communism and strained Chinese-American diplomatic relations. The re-establishment of Chinese diplomatic relations led to first-generation Chinese-American children feeling conflicted. As Orville Schell, New York Times reviewer of The Joy Luck Club phrases it, Tan shows that first-generation Chinese-Americans of the 1970s faced a "complicated interior problem: how to recognize a country to which they were inextricably bound by heritage, but to which they had never been" ("Your Mother is in Your Bones"). What's more, they had to face their internal struggle while integrating with American culture. Therefore, a second reason Tan's books are so popular is because of how well she addresses first-generation Chinese-American cultural issues, struggles that many immigrants can relate to.
As Deborah Mason (reviewer of The Opposite of Fate for The New York Times) suggests, a third reason Tan's writing is so popular concerns the entertaining details she has the wisdom to include, such as a description of her singing in a rock band made up of writers and a description of how she dealt with growing up in a home full of "[Chinese] good luck charms, and they come mostly in the form of dragons, fish, strategically placed mirrors, and heaven forgive me, New Age crystals" (as cited in "A Not-so-Dutiful Daughter"). Mason also points out some of the details portraying the cultural conflict felt by first-generation Chinese-Americans that makes Tan's writing so rich and well-received, such as the conflicts between her father's Baptist religion and her mother's Buddhist faith and ancestor worship. As a means of accommodating both the worship of the Holy Ghost and of ancestors, Tan describes that the Holy Ghost "sat at our dinner table and ate Chinese food. We laid out chopsticks and a bowl for our unseen guest at every meal" (as cited in "A Not-so-Dutiful Daughter").
As I am unable to locate a section in the table of contents of The Opposite of Fate labeled "My Mother's Secret," let's look at the section titled "the cliffsnotes version of my life" for more examples of details she chooses to add that make her writing so rich. Her wit especially makes her writing rich, and we see an example of it in the opening of this section in which she narrates her experience of being asked what she does for a living after publishing her first book. After she proudly replies, "I'm an author," she is next asked, "A contemporary author?" Her wit shines through in her next narration:
And being newly published at the time, I had to think a moment before I realized that if I were not contemporary I would be the alternative, which is, of course, dead.
Hence, as we can see, some things that make Tan's writing so popular are the way she craftily combines autobiographical accounts and fiction, reveals struggles first-generation Chinese Americans dealt with in the 1970s, includes entertaining details, and reveals her wit.