Reviews are based on your personal opinion and reaction to the film, but I am happy to help guide you in writing the review! Just like when reviewing a book, when reviewing a movie you will want to draw from specific examples in the source to support your opinion.
Opinions will differ on whether it is a great film or not, but here are some things to consider. "Good" is a subjective word, and instead you may want to speak in terms of effectiveness. Think about the genre. Is this an effective horror film? Does it fit in the genre, or is it lacking when compared to other films in this genre? What was the film setting out to do—scare the audience, entertain the audience, make the audience think, or some combination? Was the film effective in doing so? Films differ from books in that there are other elements we can evaluate, such as cinematography, special effects, and performance of the actors. You can take those factors in account when writing your review.
Before we can evaluate the theme, we must identify it. What do you think Jordan Peele is trying to say in this film? How does he explore the themes of family and identity? You will have to decide if the theme is strong or not.
Here are my personal thoughts: I thought this was an effective horror film because I was haunted by it even after I left the theater. I thought Lupita Nyong'o was a fantastic actress in portraying the anxious mother Adelaide, and Red. Identity is a theme I think he addressed, since the whole premise of the film is that the characters are dealing with their doubles. This is highlighted by the title, and by the actors playing two roles. I was surprised by the reveal at the end, and it made me want to watch the film at the end to look for clues that would have suggested the switch.