To the interpretation of any aesthetic object it is important to question for aesthetics. But if the intention it to judge a film (a past fact) as good or bad (praise or blame), of, course, the epidictical genre should be used: the reasons why it is so must be given, proved and beautifully (strongly) expressed. So, the discourse has to be written with style, since the epidictic genre has more connection with literature than with argumentation. The deliberative discourse talks abou future, as politicians do.

Luisa, thank you very much for your prompt answer. I'm still wondering whether the main intention of film reviews, as a kind of opinion forming and persuasive discours, could be considered as deliberative since the jounalist wants to persuade his readers to go and see (or not) the film.   

Any type of rhetorical discourse is persuasively oriented. The scope of rhethoric is PERSUASION. As Aristoteles states: “rhetorical study, in its strict sense, is concerned with the modes of persuasión”. I recommend the first book of Aristotle Rhetoric to you, as well as Corbett’s Classical Rhetoric for the modern Student (a great book). 

Dominika, contemporary takes on epideictic point to its values function: epideictic helps social groups cohere and maintain by clarifying and circulating values (Graff & Winn, 2006), and by arguing for one values hierarchy over another (Marcellino, 2013). To the degree that film reviews reflect values hierarchies, they can be parsed as epideictic.  A good current example is the film American Sniper--reviews of that film may involve fine technical points and thus have a forensic dimension, but the majority of reviews are about how the film portrays violence, American military action, and military members, and the values stakes in such portrayals.

Hope that helps.

I would like to thank you both, Luisa and William for your interest and all the comments and remarks. They have clarified many relevant aspects of the problem.  

Thank you Neill for your opinion. Well, I also do think that the main dimension of a film review refers to its deliberative function which also consists of epideictic elements. So, the journalist analyse a film in terms of its artistic values and technical skill (and so forth)in order to persuade. Thus, the overall purpose of film reviews should be a recommendation on whether it's worth spending time and money to see the film.

(At least, that's what I need to do when I work on my own film rewiews. Otherwise, my boss won't accept it :)

"Despite this overlapping of kinds of discourse, however, ceremonial or epideictic discourse is a distinct type. It differs from deliberative discourse in that its primary obtect is yo praise or censure someone, not to persuade others to do or not to do something" (Corbett dixit, p. 139).

Of course, genres of discourse do not have categories with discernible borders; they work mixed.

There is a genre continuum in film reviews between clearly deliberative ones and clearly epideictic ones. Ordinary moviegoers tend to treat reviews as a tool for deliberation. Thus most user created reviews you find online have a quite explicit deliberative slant.

At the other extreme professional film critics, film theory scholars, aspiring film philosophers and general film-nerds-with-way-too-much-time-on-their-hands will be on the epideictic side.

Audience design plays an important role in deciding whether the discourse is epideictic or deliberative. The film theory scholar or dilettante largely speaks to people who share her/his enthusiasm for cinema and are supposed to have watched the movie (and the countless other obscure movies that are cited in the review). The run-of-the-mill online review addresses people who have to decide whether the movie is worth watching. Explicit preoccupation with "spoilers" is a clear sign of this audience design and of a deliberative function.

Professional reviewers writing for newspapers and non-specialist magazines fall somewhere in between. They know that their readers will use their review as a deliberative tool. However, also in order to maintain their ethos of experts, they will dress their review more as an epideictic exercise that as an explicit advice. They will carefully avoid spoilers, but they will not mention the issue of spoilers explicitly.

Yes, I can truly agree that the audience plays a crucial role in choosing the right genre. Every discourse, if it wants to be comprehensive, must be prepared with respect to its potenial readers. That's what P. Charaudeau claims as well.

http://semen.revues.org/2793

film is genre in literary because leterary as fiction is imaginative, film that imaginative are literary