I think the entire thing was a mess of some good, but mostly bad ideas, performance, characterization and especially aesthetic choices that just weren't good.
I've said this before regarding his performance, he went from good to horrible in the course of single sentences, let alone the entire performance. The whole performance was inconsistent with highs and lows. I think it's one of the most un-even performances I've ever seen, especially from an actor that clearly has alot of talent and potential, even in this role.
They made him love sick for Harley, that's one part of it that's "Not Joker", they made him too public of a character, seemingly owning a Nightclub over his more traditional abandoned hideouts, he's known to make public statements and very public crimes, but keep to the shadows while during his planning/downtime phases to avoid his acts from being prevented or predicted by Batman, not chilling in the VIP of his own nightclub where Batman can just walk in and take him down anytime he wants. They made him materialistic with flashy clothes, jewelry and cars, when typically the Joker isn't concerned with those things for the most part. He also had no arc of his own in the movie really, just that he's trying to rescue the girl he loves, which again, not the traditional Joker/Harley relationship.
I still think Leto can be a good Joker but there needs to be alot of retooling of the characterization, writing/dialogue, motivations and aesthetic, along with giving him his own villainous plot this time around. I'd still be up for seeing it, I think Matt Reeves could get something out of Leto with some tweaks.
