People come to read the reviews we read for information on a product, a movie or what have you. They want to read the good and the bad on the subject so they can make up their minds whether they want to try it or not.
In writing a review it is necessary to give as many pros and cons on the subject as we can think of. The review should also be written with a title that grabs the eye and then content that goes with the title. In other words dont give it a title that has nothing to do with the subject matter as that is mis-leading and will not get your review rated and will not help the consumer.
You do not need to write a book to write a good review but you need to put some thing useful in it and in a lot of cases research.
Lets take the subject of a web site. We will use as an example https://pogo.com as I have already written a review on that site.
Before doing so I went and used the site, made notes and tested it out for a period of time.
So now I am ready to write the review. A bad review would be, This is a really great site, you can play all kinds of fun games, win tokens and a chance at winning money
How much does that tell the reader? Not a heck of a lot. Now if I tell you all the games there are and how they are played and go into all the details I know then you will probably be interested in checking out the site.
Never write a review just to add one to your total. Also dont write one if you dont have enough facts to supply. If you use a web site and know everything that goes on there, then write about it. If you go look at it for 5 minutes dont try writing a review until you can make it more informative.
The same goes for a book review. I can tell if some one has read the book or if they read the summary on the cover and wrote about that, and everyone else can also.
Write the best you can, and put something of yourself into it.