If this film paints the Joker as a sympathetic character without showing his true evil nature at the end, then it will have missed the mark by a mile. It needs to show that he wasn't the poor victim we all thought he was all along. That he's actually the villain of his story. I hope they don't screw this up.
While I am very interested in seeing what they do with this, I agree with you that this has to be a balancing act where on the one hand we empathize with the guy but on the other hand we also can see that while he may be beaten down, we know that he takes things too far and that as bad as we feel for him we can't empathize with him terrorizing/ killing people. There has to be a sense where even he knows what he is doing is wrong and but he just can't help himself.
I love the look of this Joker too. A really cool interpretation of the iconic clown make up and the suit is just fantastic.
There really is something about the swagger he has when he walks out of his apartment and comes down the stairs splashing in the puddles as if he owns the entire city. His body language alone when he's in the makeup vs. him as a regular guy it's clear he's like a different person.