Huh...
I've been impressed with Affleck's recent film work, as director and actor, but I'm disappointed by this news. I really think the film would've worked better casting a no-name who could both pull off the role as well as the fantastic combat and stunts required. The film was going to do billion dollar numbers anyway...it's Superman vs. Batman for Christ's sake. Everyone and their mother will go and see it. It didn't need a big name actor to draw people in.
While I'm sure Affleck can do a decent job, I'm unsure how well his voice will work for the Batman persona, for one, and not sure he can do the somewhat cantankerous, seen and done it all bad-ass that Batman is as he was portrayed in The Dark Knight Returns, which this is supposed to be drawing from. Even though it will be changed and not a carbon copy of the comic, the casting rumors of them going with an older Batman lend credence to the idea they're going to use the Batman and Superman interplay from that book as a guideline to their portrayal here. And I think that'll be a good thing, not only for an added sense of dark humor for the film, but also as a way of taking Superman down a peg or two after his messianic, saving the world stature he has after MoS.
Eh, we'll see. I still think Scott Adkins could've done a superb job with the combat. Affleck, much as I like the guy, kind of indicates we're in for more of the same in regards to the combat: quick cut close-ups and overall unimpressive.