Oh my, oh my... It is hard to explain what I think of now, after reading this book. It was magnificent, brilliant, priceless. I am afraid that I am so engrossed with this story that I am not capable to write an appropriate review. 
 First of all, it is a phenomenal study of human being. Our feeling, especially fears and prejudices. It is so amazing how Rhys caught deep true in a relationship between Antoinette and Rochester. 
 Nothing left but hopelessness.' Say die and I will die. Say die and watch me die.' 
 It was simply perfect. And of course issue of slavery... 
 Secondly, it is a good historical fiction. The world of Jamaica (and Victorian rules) was described interesting and very engaging. And the clash between "wild Jamaica" and "civilized world" was an excellent parallel for the clash between Antoinette and Rochester. 
 Even if you don't know a story of Jane Eyre (although it is hard to imagine ;-) ) you will find 'Wide Sargasso Sea' remarkable. 
 And, if you know the story of Jane Eyre you will appreciate how genial Rhys created Rochester's past. It was not only logical but most of all beautiful that I am feeling like I would have been struck by lightning. 
 She had left me thirsty and all my life would be thirst and longing for what I had lost before I found it. 
 Really, I don't know what to tell you more. I have read it in one sitting. 
 I know this book has very different reviews. I belong to these readers who love it and I agree e.g. with Paul and Bookdragon Sean. I recommend their reviews if you have any doubts - read them.