granting the audience the feeling of happiness they've been awaiting for two hours.
@carcass
I feel relief fits exactly well as the same way catharsis fits in the blank. But again when i reread the sentence i paused at the apposite phrase "eventually showcasing the elimination of all the protagonist's abusers". So now I am really okay with catharsis.
personal opinion. Any second thoughts carcass?

In my view: you do not wait for a feeling, it arose at any moment.

Since the audience waited for it for two hours, then catharsis is more suitable.

The only thing I could think about.

Regards

Blank (i) Blank (ii) Blank (iii)
(A) fairness (D) catharsis (G) embellishment
(B) slavery (E) relief (H) denouement
(C) injustice (F) inconclusiveness (I) platitude

Fairness, relief, denouement

kudos

The new film, though a chronicle of exploitation and iniquity, nevertheless is deeply concerned with notions of (i) ________ , eventually showcasing the elimination of all the protagonist's abusers, granting the audience the (ii) _________ they've been awaiting for two hours. Despite the satisfying up­heaval, however, the plodding plot en route to this (iii) ___________ leaves much to be desired.

The sentence fragment:

eventually showcasing the elimination of all the protagonist's abusers

ensures that the word for the first blank is fairness.

Since it is a chronicle of exploitation and iniquity which finally eliminates all the protagonist's abusers, which the audience has been waiting for two hours, it grants the audience catharsis.

catharsis is the process of releasing, and thereby providing relief from, strong or repressed emotions.

Since all the abusers of the protagonists have been eliminated, the plot is plodding to its denouement.

Denouement is the final part of a play, film, or narrative in which the strands of the plot are drawn together and matters are explained or resolved.