I read this book in French, "L'Art Du Roman" and while it does not attempt to reduce Kundera's works to neat theories, it does shed light on the philosphical underpinnings of many of his novels.
In fact, one of the main themes of this book is the critique of reductionism. He exalts the "Wisdom of Uncertainty" and eschews any art work that proceeds from an ideology or moral high ground as such leads to judgement rather than understanding. Somewhat in an existentialist vein, Kundera promotes the idea of "l'ambiguite" as the ideal for the novel. That is to say that given we live in a world where there is no right or wrong way to proceed, the role of the novel is to understand each character within his own constructs, not according to some extrnal morality or ideology.
Kundera's debt to Heidegger is made obvious throughout the book, and Kundera quotes him often. One is left wondering what Kundera's ideas on morality might be. However, I would not go so far as saying that he follows suit with Heidegger on this mattter. Heidegger's "Sein und Zeit" is interested in the question of being. For Da-Sein, morality is secondary, and relativistic, not primary and essential. No doubt, this indiffference towards morality led to Heidegger's nazism. However, if Kundera does not take a moralistic posture in "unbearable Lightness of Being", he defintiely implies that we suffer or thrive on a spiritual level with certain choices that we make....
-Thomas Seay