The longer the movie went on the less I could believe that Arthur was capable of accomplishing anything. By the time the climax comes and he stands tall and triumphant I just didn't believe it, didn't felt earned. It felt like we got there because the movie was ending and we had to get there.
Now in all the Joker related media I've consumed in my life Joker has been Batman's foil, but I just don't believe that Arthur's Joker can be a anywhere near a credible threat to anybody, let alone Batman.
I could appreciate that technically it is a well made movie. The acting was good, it looked good and sounded good. So I supposed that the answear as to why I disliked Joker is that I had an idea of what the Joker is supposed to be and Joker wasn't that. Instead of being enthralled by the movie the more it went on, I found myself loosing more and more interest the longer it went on.