A lot of the critics who has been laying into the film have raved about his performance. I think people want to dislike Ben Affleck, but most things he has done recently have been pretty good. Gone Girl, Gone Baby Gone, Argo, The Town etc. Personally I'm not a huge fan of Christian's Bale Batman and was more of a Keaton fan myself. Although, I think the Batman from the animated series is pretty fantastic too
As for Ben in this movie he was a great Batman and Bruce Wayne. I thought Bale was a good Bruce Wayne but a shitty Batman. Affleck was dark, brooding, and tormented, but while being charismatic and aloof. He was Batman. Couldn't ask for much more. The movie itself...not so perfect.