Book reviews will primarily be under consideration here nevertheless, several of the principles mentioned will apply equally to reviews of other products.
What are reviews?
In effect these are an extension of word-of-mouth recommendations or warnings which, most will agree, is the best vehicle for such communications. However, in these technology led days it must be acknowledged social media e.g. Facebook, Twitter, Google etc. are not only extensions of but often replace face-to-face, word-of-mouth, interaction. Whether or not this is good for society is another topic not the subject of this discussion.
Who are reviews for?
Are they for the author/creator of the product or for the purchaser/consumer? The reply frequently depends upon who is being asked. To answer the question accurately the purpose of a review needs to be addressed. In principle a review is usually posted/published as a means of assessing the effectiveness; value; relevance and adequacy of a product. It follows therefore they are most relevant to prospective purchasers/consumers. Of course that does not mean an author/creator cannot learn from them. Reviews frequently enable them to see where there may be shortcomings or omissions or a need for further development or improvement, etc. They may also be encouraged when they have got matters right and are given praise for a good quality book/product.
What is wanted from a review?
As stated at the start, the perspective for this discussion is primarily that of books. The following are a combination of common-sense and reader/author observations. Remember, though the following points principally apply to book reviews some will also apply to reviews of other products.
Honesty: Far and above anything, everyone, readers and authors, want the reviewer’s truthful and sincere opinion.
Clarity: Not a long winded resume that says little about the actual book or product.
Details: Brief overview of the book without simply regurgitating the synopsis and avoiding the inclusion of any spoilers (giving information about the content that will spoil it for potential readers).
Likes/Dislikes: The personal observations of the reviewer. Except for technical/tutorial books reading is a subjective experience. Readers of a review like to know how the book impacted upon the reviewer as an individual. Naturally, as each person is different, there may well be inconsistency across multiple reviews.
Quality: All reviews, no matter the product under consideration, should reflect upon the overall quality. For independent, self-published, books, grammar and editing are important aspects potential readers like to hear about.
Style: With books the; style of writing; originality; character development; plot structure; etc. are relevant topics potential readers will be interested in.
Comparisons: How does the book or product compare to other similar books/products.
Value for money: Self-explanatory.
Rating: Virtually every site, social media or business, tends to incorporate a rating system (usually stars) that may act as a quick overall reference for the readers of a review. Further information about ratings may be read here.
Language (Terminology): Reviews should be courteous and polite even if negative. It should be born in mind anyone may read a review including such people as elderly ladies and children. Bad language is not necessary and actually reflects more upon the reviewer than the product.
Recommendation (Optional): Both authors/creators and readers/consumers, appreciate an honest, personal statement by the reviewer: Hopefully a recommendation. Of course, it may be they cannot recommend others purchase the book/product. Though this should have become obvious in previous comments, the reviewer may, if they wish, add a recommendation not to buy. This is a personal decision.
Reading is primarily a subjective experience. Consequently, one person’s perspective and appreciation, or otherwise, may be very different to another’s.
Authors/creators will often state what they would like from a review. Of course anyone who has produced something likes to know how it is received. But the reviewer, as well as the author/creator, should bear in mind who reviews are for (already discussed above). Much may be learnt by the author/creator but that should almost be incidental.
A general observation: The number of reviews given compared to purchases is normally very low. This may be frustrating for an author/creator but they should avoid badgering people to leave them. A gentle, innocuous, request, included at the end of a book, on a website or as part of a publicity/marketing event is acceptable but nothing more.
Note for Authors: It appears even indie (independent) self-published authors fail to post reviews of fellow author’s books they have read. Rather poor considering they expect others to post reviews of their books. It is simply common courtesy and respectful to take the time to write and publish a review.