If the final scene has you sniffling and reaching for the Kleenex, the movie you’re watching could be described as affecting, meaning it makes you emotional.
You might be familiar with the noun affect, which refers to a feeling or emotion. Affecting is just the adjective form of that word — so you can probably guess that it describes things that provoke strong feelings or emotions. You might watch an affecting basketball game, for example, or see an affecting performance of a play. The feeling caused by something affecting can be good or bad, happy or sad. The key is that it stirs up a strong feeling.