I'd disagree that Val was a terrible Batman. He wasn't Keaton but he had his own take:
I believe Clooney could play a good Batman, but one where Batman is meant to be much older, more at ease with his identity. Of course out of all the Batman he's the most off-beat of them all but with the right script and direction Clooney can do a good job. He had some touching moments with the Alfred-dying-from-McGregor-Syndrome subplot, where an aged Bruce has to confront the fact that his old servant won't be around for much longer.