This book is an excellent defense of the first amendment write to freedom of expression. It's also an excellent argument in favor of utilitarian morality. It's probably worth a read if your interested in these areas, but I felt the whole time that I was simply reading things I already believed and felt. If you're pro first amendment and in favor of being decent to your fellow humans, regardless of any differences you might have, this book won't shatter your world view.
It does get interesting when Mill tries to draw the line between an individual's rights and the rights of a society. It's a pretty standard case of your rights ending when they infringe upon mine own. The idea was revolutionary for it's time, and still isn't wholly adopted by the world at large. It's interesting to see a clearly brilliant man fumble through the question of when it's okay for a government to take an action against it's citizenry. It seems to me that Mill wants there to be a clear cut and easy to follow formula, but these things by there nature require a great deal of gray area to work within.