Regarding your assignment to write a review of the film adaptation of The Great Gatsby, I don't think it would be dishonest for you to refer to reviews of the movie that came out in the year 2000. The best sources of movie reviews by far are in Weekly Variety and The New York Times. (The Los Angeles Times also has good film reviews, since Los Angeles is the capital of the movie world.)
In addition to picking up some good ideas from topnotch professional reviewers, these reviews contain a wealth of information about the production, including the names of all the characters with the names of the actors who played them, the director, chief photographer, screenwriter, and so on. Weekly Variety should be available in the Periodicals Department at any good library. They get their information from press kits sent out by the publicity department of the studio that made the picture.
I don't see how it is possible to write a movie review without referring either to the studio's press kit or to Weekly Variety, because it is nearly impossible to catch that information off the crawler at the end of the picture. The attendant at the Periodicals Department ought to be able to look up the right issue on the computer. You would probably have to read the review on microfilm, but that is good experience if you haven't done it already. You can even take a photograph of the review on the machine.
In order to analyze character portrayal, you will need to know the names of the characters and the names of the actors and actresses portraying them. As far as the analysis is concerned, that should be a matter of your own reaction. You can compare the portrayals with your impressions of the characters in F. Scott Fitzgerald's book and also compare them with portrayals in the earlier film version of The Great Gatsby. This much should definitely be based on your own tastes, opinions, and impressions--your likes and dislikes.