Don't I have a right to express my opinion without fear of being sued for libel or slander?

Yes, so long as your statement of opinion is just an opinion, and does not contain specific assertions of fact that can be proved untrue. For example, "I didn't like Star Restaurant. The wait staff is slow and the food is too spicy," is a statement of opinion. "Whatever you do, don't go to Star Restaurant. I had a hamburger there that was tainted with e.coli and had to be hospitalized for a week," is potentially a defamatory statement if, in fact, the restaurant can prove that you never contracted e.coli and never spent any time in the hospital after eating there.