You can give your opinion for any of the movies, books or music on many websites that ask for reviews. By offering your own thoughts on the different entertainment finds, you are helping others decide on their next outing, music or book purchase.
These consumer reviews websites can be quite helpful, not only in the entertainment topic, but also for any products you've used. If you can offer your advice on what you recommend, people will read what you have to say and appreciate that you took the time to offer these reviews. book reviews are especially appreciated as many don't want to invest hours or days reading a book that is not enjoyable.
While on these sites offering your own reviews, you may also read reviews from others. These opinions may just help you in your next choice in reading material or movie outing.