I've read a number of pieces about this film now, and it's remarkable to me that none suggest that Nicky has any sort of mental health issue. He's 'frantic' or 'frenzied' (etc.) and he probably is not a stranger to various substances, but there's quite clearly something else going on.
For a mediocre filmmaker, a scene in which a man tries to talk his friend into hitting the road to evade the mob would be a moment of routine necessity to prepare the audience for a set piece. For May, however, such a moment is the set piece.[…]
Another instance [of] violence, involving a bus driver, erupts later in the film, which May invests with a mischievous streak of comedy. Such scenes deflate the masculine pomposity of the common crime film, showing violence to be, well, violating, as well as ludicrous and pitiful.
[…]
Few films have so exquisitely captured how straight American men reveal their affections and insecurities to one another, as well as how they’re both threatened and awed by each other. It becomes evident that Mikey is the drab runner-up to the sexy and charismatic Nicky: the reliable beta to the latter’s commandingly reckless alpha. Mikey’s betrayal of Nicky has a resonance, then, suggesting a loser’s opportunity for revenge and grace. Yet this resentment is always understood by May to be girded by an authentic and inescapable love.
— Chuck Bowen (Slant Magazine)
It’s a betrayal with many fluctuations, hesitations, reversals, and ambiguities, and May might be the least sentimental woman storyteller since Flannery O’Connor in her stark refusal to sweeten the pill.[…]
It was released after a dispute between the studio and the writer-director about the two years she’d already spent editing the 1.4 million feet of footage she’d shot [—] one can start to appreciate the sheer mass of the footage involved if one considers that 475,000 feet were shot for Gone With the Wind.