Not possible to fully pull this off

Rating: 7/10 (13 January 2020)

I do acknowledge that there was great effort that Phoenix put into the role, especially the weight loss.
But a vast majority of this character study asks the filmmakers to express visually and verbally what is happening mentally. Film is a demanding medium where you have to constantly keep the train moving. And to dwell on long verbal exchanges to pinpoint the character would not be acceptable to an audience. But it's what was needed to approach a more authentic portrayal.
A sliver of that was when at the hospital he vaguely admitted the three murders on the subway. He thought it would bother him but didn't. Where it wasn't done was after he realized the girlfriend was a delusion. No real reaction.
An unrelated attempt was Negan from The Walking Dead. There were glimpses of reason in the writing but the character started off so annoying, it was a failure from the start.
Although a completely different tone, Heath Ledger's Joker take was more interesting and compelling. He was already in the madness but you had a sense of pain in his past.
To me, it felt that Phoenix was struggling much of the time. The "dancing" was the quick way to add an uncomfortable visual to the character. The laughter didn't seem right as was more annoying than uncomfortable. Someone like him went towards a need for power in our lives, like anyone. There was never really anytime of weakness, asking for help and being fearful of losing everything. All that was left for Phoenix was to accentuate the lesser, but visual, elements of the character. Sometimes those were over the top.
So the story was a series of incidents that started to tear away at that "power." If anything, what I saw was a series of coincidence. We were just going to the next and next and next until the eventual break. I didn't get the feeling of a gradual descent into madness. He was already significantly mentally ill and didn't get worse. He was just shown he didn't have any power to begin with and thus made a decision to go the route he went.
A couple quibbles of details was Randall gave Arthur a gun as one character and then ended up suddenly another. Arthur pointing the finger at Randall as owning the gun was forced.
The mother ends up as previously being very mentally ill. But I saw no sign of that in the portrayal of her old.
Also the detectives said they found out Arthur asked someone if he could buy a gun. That was not shown. Was that Randall trying to sell a lie to the cops?
Arthur's "relationship" with Sophie didn't ring true and I clearly knew there was something wrong. So if they wanted that to be a surprise when it was shown to be a delusion, it didn't work. Also, Arthur didn't seem to demonstrate other visual delusions.
Surprised I was disappointed. It did try hard to shoot for the stars.