I'm not excited about the news of Affleck as Batman, but I'm not going to cry myself to sleep over it either. Mainly because I'm not much of a Batman fan, even though I loved the Keaton and Bale movies. Hopefully Affleck does well enough that we can focus on whatever the actual story is, because the story is what will make or break this movie I think.
As an aside, I find it amusing that there are all these lists of actors that people hated when cast, but knocked it out of the park with their performance, and never any lists of actors that seemed fine for the roles but sucked out loud when all was said and done. That's probably because people just write it off as a bad movie and it is hard to quantify performance vs. shitty movie, but you see my point. We only ever talk about the few times everything turned out better than expected, not the multitude of times it failed miserably.