Alexander completely nailed his role in this film. He makes you want to hug him just to let him know he's not alone. For acting to hit you on an emotional level that hard they must be doing something right.
Alexander (Leo) plays a mute man in search of his love interest. Obviously when you're scouring a city looking for someone, not being able to say a word makes it difficult. You're isolated and looked down on. But Leo is loyal to a fault and nothing will stop him.
I've always loved the gritty, dystopian future aesthetic in films (ie: Blade Runner), and they've done pretty well here. It's just a shame you don't get to see too much of it. Most of the film is isolated to certain spots and inside buildings, so you don't get to see a lot of the city. Budget thing perhaps?
I enjoyed Paul Rudd's performance, too. While he is hot tempered and his choices come across unscrupulous, he actually does show signs of having a moral compass in certain situations.
Overall, I thoroughly enjoyed Mute, and I've seen it twice now. My only complaint is it does seem to fall flat, as if it were hastily written. It's an excellent premise for a story, but it just doesn't quite bring it home the way it could have.