Warner Brothers got their high-brow character study and DC tacked their name on it in hopes of landing something that would give them credibility in the ongoing game of comic book movie king of the hill. Sorry guys, but you both missed the summit and only ended up with mud on your faces.
On the plus side, this is a deeply disturbing, and brilliantly acted, journey through the troubled and increasingly damaged human mind. Pheonix's performance, though occasionally grating, is award-worthy. This is a very troubling character study that would rank among the very best independent art-house offerings.
On the minus, this isn't honestly related to the DC universe in any way, shape, or form except through the ill-conceived, and obviously economically driven, power of branding. Nothing about this joker meshes. (And yes, I said joker, not Joker, because all this wretched clown is is a common charlatan trying to be something he's not.) He's not who we know the character to be nor how he fits into the world around him,
We're given no clue that he's any sort of criminal mastermind, or honestly that he's even very clever at all. From the glimpses into his journal, it actually truly appears that he operates well below the average even, which is what we see in his behavior as well.
This is not an arch-villain, or a mad-genius. We're given someone off their meds and denied government assistance, which is all it takes for them to finally realize that they're Stuart Smalley with no remorse and an itchy trigger finger.
And one point that proved even more that this in no way fits in with the Batman / Joker mythos is how they tried to force them together here. Almost like duct-taping two magnets together along the same poles so they can't repel each other then claiming that they mesh. We're introduced to a young Bruce Wayne, who appears to be perhaps ten, when he meets this soon to be joker, who is very obviously easily in his mid forties. Given this, by the time Batman will first face his arch-nemesis, the Joker may well be drawing Social Security.
Again, this film is a lot of things, but it has no business shoehorned into the mythos of DC's tentpole character, other than a corporate decision that the branding would make money. As a film study, or a character study, it's well worth it. As entertainment, it's extremely debatable. The theatre I was in emptied with silence or muttered grumbles. As a part of the DC universe or Batman's Rogue's Gallery, it's a disaster.