My unpopular opinion: Kilmer was a decent Batman .
Sure, he wasn't given the greatest material and he didn't have a Chris Nolan to guide him, but I felt he did fine with what he was given.
At the time , i.e. 1995-96, he felt the closet to me to the Animated series Batman in live action. He was a hero as opposed to an avenger, he had something of a code however thin, and he looked like the Dashing and charming playboy.
His version is uneven, though I feel that has more to do with the script and direction then Kilmer's performance.
I think feel he either gets lumped in with the trainwreck of Batman and Robin or he gets ignored, forgotten, or dismissed all together.
More people tend to talk about Clooney than they do Kilmer.