You can't beat Kundera for a novel of ideas, though he is rightly accused of lapsing into platitudes or drivel. At his best he weaves a complex but seamless and sexy story from many threads, the threads being the characters and politics and metaphors that personify and situate and exemplify his ideas. This is Kundera at his best.
There are many directions for a review of this book to take, and plenty of professional reviewers who have covered just about all of them. I'll just note that what Kundera doesn't do in this story is as important as what he does. He does not let Tomas (or anybody else) off the hook for being an asshole, which he threatens to and easily could, given the book's premise:
"Let us therefore agree that the idea of eternal return implies a perspective from which things appear other than as we know them: they appear without the mitigating circumstance of their transitory nature. This mitigating circumstance prevents us from coming to a verdict. For how can we condemn something that is ephemeral, in transit?"
Sounds like a page from the sexy smart guy's guide to getting away with just about anything, Tomas being a sexy smart guy whose favorite pastime is seduction. He plays at love like playing poker, and oh baby can he bluff.
But Kundera makes you want to defend Tomas as much as you'd like to slap him, in part because Tomas is capable of really if ineffectually loving, but also because it seems that a defense should follow from the premise. It doesn't, because the bottom line is not transience but paradox, and it's a fine line. Humanity walks it like a fine line: stumble one way and we're nothing but assholes; stumble another and we're nothing but kitsch, and ultimately neither will do. I consider this a brilliant exploration of the human predicament and his sexiest story.