I'm cautiously optimistic. If I can go from disliking Chris Evans in Fantastic Four to liking his performance in Captain America and Avengers then there is hope. Ben Affleck does have experience in portraying a Super Hero (Daredevil). I think he can definitely pull of Bruce Wayne, I'm just wondering about the alter ego.
One of his friends by the name of Kevin Smith, knows a lot about Batman. Comic Book, animation and live action versions. He's got that line of advice.