At first I was shocked at Ben Affleck being Batman, then I remembered the biopic about George Reeves as Superman and he did an excellent job and got a couple of nominations. Plus not to mention he does bear a resemblance to the Batman we see in Arkham City and would look even better if he bulked up a bit for that role, but we shall see.
Like any movie, all that matters is the script that will either make him or break him. Plus it's already confirmed he is doing multiple Batman films past Man of Steel.