Note: As you can see from every series for Persona 3 the Movie, this Makoto Yuki character personality changes(+adds) from every movie to movie. Instead of just using personality from one series of movies only, writers will use the final personality (combining #1 to #4 personalities).
Makoto is a silent type of person aside from technically speaking in battle in certain instances. While being a silent protagonist, he is very stoic, reserved, and calm, gathered by the fact that he remains unmoved even when guns are pointed at him. He appears very introverted, distant and aloof since he only observes the conversations from far and only speaks when someone is directed at him for his opinion on the matter. Though he's quite introvert, he's trying to strike up conversations if the situation between him and his interlocutors becomes pretty empty or awkward. If he failed to do so, he chooses to go somewhere by his own, leaving the interlocutors by themselves or in rare case, he'll ask to go somewhere instead of standing face to face.
As you can see from the movie 3 halfway end to movie 4, Makoto has slightly changed from the closed type to open type. Though he's a stoic, emotionless one, people will find that he can easily expresses his feeling through the changing expression on his countenance although he would obviously hide it so that people won't be able to see his expression.