Hard to say, I agree with the consensus that Jared Leto’s performance was forgettable, but there are several things I think Leto did well during his tenure as the Joker.
Above all, I think he played the “crazy” side of the Joker well.
Certainly, his “madness” is different from other Joker versions of “madness.” For example, Heath Ledger’s Joker was insane in that he was obsessed with Batman to the point of insanity, which would lead him to do things like this.
Joaquin Phoenix’s Joker’s insanity came from his mental illness and making him laugh randomly and completely out of the situation, which I think is his main source of insanity.
(This photo is beautiful.)
And Jack Nicholson’s Joker was, well, Jack Nicholson being Jack Nicholson.
Granted, Jared Leto’s insanity didn’t work as well, but I thought it was pretty good. Rather than a probable cause, Suicide Squad’s Joker’s insanity can be attributed to complete mental instability.
(Lying in a circle of knives.)
(Randomly torture Harley Quinn.)
(Making his minions wear animal masks.)
etc etc.
This part of the Joker was very well represented in Suicide Squad.