My only major gripe with this game is that the protagonist doesn't speak much at all when I feel he should be. It kind of makes some scenes feel like a one-sided conversation where the girls are rambling to themselves.
You make a good point. My goal is to make the player character a fill in for you, the player. Giving him a strong personality could contradict with the player's personality, or maybe he could say something the player wouldn't agree with. The protagonists are actually the girls, not the player, so these things are deliberate. However in the newest events I've decided to give him more of a voice. But he'll always be "the silent type" so that the player can fill the PC's shoes as much as possible.