The trouble with the term "erotica" is that it is used as a marketing device to describe everything from highly literary fiction to pornography. Generally speaking, readers who enjoy literary fiction don't enjoy pornography, and vice versa. When one reads a work of "erotica," therefore, one is always taking a certain risk. (I'll admit that the same thing is true in other genres -- "fantasy," for example, could mean anything from mind-bending mythology to sparkly vampires.)
Cecilia Tan's work is clearly serious fiction that is highly erotic. She is concerned with issues of identity, agency, power and responsibility. She cares for the long-term happiness of her characters. She has a larger agenda.
For example, "The Little Mermaid" has always been a potential venue for erotic exploration because of the tail vs. legs dichotomy. But in Tan's hands, it becomes a medidation on the fundamental elements of life, the primal need for connection and passion, and the inability to silence the voice of one's needs once they have been awakened.
Similarly the science fiction piece "Now", which could simply recount a sexual ritual, instead explores the dynamic of love that cannot be fulfilled, where sexuality serves as a temporary and ultimately incomplete substitute.