Exactly. It's not like this is the first time we've seen Bruce Wayne portrayed by an actor with dark hair and a decent build; Bale's hair color was maybe a couple of shades lighter than Affleck's. As good as our former on-screen Batman was, though, he never quite looked like his comic book counterpart.
I think just about all of Affleck's recent predecessors in the role have a more distinctive appearance than he does: Bale has hawkish features; Keaton and Kilmer are almost infamous for their sort of "pouty" look under the cowl (a fact not lost on the satirical publication, Mad magazine). Affleck, however, much like a comic book drawing, has this kind of square-jawed, generic countenance.
I can't speak for everyone, but, for me, that's why the guy looks so much like Bruce Wayne/Batman. As he continues to improve on his physicality through exercise and such, said resemblance will naturally be taken a few steps further. That could explain some of the positive reaction (to newer pics) we tend to see on the boards of late.