Objective: To provide details or your opinion on the novel, film, documentary, product, service, etc.
Intended audience: depending on the task
Style and register: formal or informal. Depending on the audience
Structure:
Introduction: A summary of the reviewed material. General information such as author, director, dates, etc. Do NOT give hints of the plot or the reviewed material at this point.
Body:
Paragraph 1: plot, characters' names, more specific details about the story, technical specifications if it is a product or a service. Avoid giving your opinion along these lines.
Paragraph 2: highlight the good points
Paragraph 3: highlight the bad points and/or areas of improvement.
Conclusion: general impression. Sum up the good and bad points. Recommend readers from seeing/reading/attending/buying it.
REVIEW SAMPLES
How to write a review | Writing Essentials
How to Write a Literature Review: 3 Minute Step-by-step Guide
FCE (B2 First) Writing Exam - How to Write a Review