I find shy, introverted characters endearing. And Joaquin Phoenix's character fits the bill, looking much like a mustachioed Leonard from The Big Bang Theory.
I can't tell if this movie is going to be profound or perverse.
If the AI is an actual mind, and not a program meant to simulate a person, then falling in love makes sense, since you have to minds (souls) making a connection.
But if it is just a program, then I think this could be an interesting reflection for our Siri-soaked society, where the line between illusion and reality blurs and we mistake artificial intimacy for the real thing.