I first read this book when I was about 16 - I loved it then and I still love it now. Although its basically just a romance, it stands out for me because of the characters and the setting. What's great about the lead characters is that they're very flawed, but you see them recognising and dealing with these flaws over the course of the book, and despite their faults they are both very likeable.
The heroine, Hero Frost, is a beautiful but quite cold and priggish do-gooder who goes out from Boston to Zanzibar to try to bring an end to slavery. As the book goes on, she starts to realise that things aren't as black and white as she's always thought and you really see her character to mature and to become more open and warm. Her relationship with the hero, a charismatic but cynical Emory Frost I really liked - I completely understood their attraction for each other despite their obvious differences and I loved the development of their relationship.
Another thing I loved about the book is the setting. You learn so much about Zanzibar, its people, politics and history that it almost another character - I've been desparate to go there ever since I read the book! Definitely, I'd recommend this book as a great read if you can get hold of it.
SPOILER BELOW
I've read reviews criticising the rape scene in the book. However, this scene (which by the way is implied not described - there aren't any "sex scenes" in the book) made complete sense to me in the context of the book, and I certainly don't agree that it condones rape in any way - in fact, you actually see one character commit suicide because of her rape. When you read the book you can understand (although not agree) why Emory acts does what he does. For me, what the author does is to take subjcts like slavery and rape that we all find repugnant and look at them more closely.