For the two-plus seasons I watched "Nurse Jackie," it was a show with a tremendous lead performance by Edie Falco, a bunch of well-etched supporting characters played by Merritt Wever, Anna Deavere Smith and Peter Facinelli (among others) and a reliably black comic sensibility that could deftly turn on a dime for more serious moment. But it was also a show that, like Jackie — a painkiller addict concealing her addiction, an extramarital affair and any number of other secrets — stubbornly, proudly in denial of the need to change things up even a little. Consequences seemed to hurtle at Jackie with regularity, but they were always quickly dodged.
 
After a while, that refusal to shake things up and force Jackie to deal with the wreck her life had become forced me to quit the show cold turkey. After I left, things got even worse on the no-consequences front, as last season's finale (which I later watched on a "Even you won't believe they did this" recommendation from a friend) went out of its way to tease anyone who thought comeuppance was coming. On the personal front, right when Jackie was on the verge of confessing her adultery to husband Kevin (Dominic Fumusa), he admitted an affair to her, allowing her to hypocritically reclaim the moral high ground, while at work, Ms. Akalitus (Smith) threw Jackie's drug test in the trash to protect her.
 
But sometime between that finale and the fourth season premiere (Sunday at 9 p.m.), "Jackie" co-creators Liz Brixius and Linda Wallem appear to have had a moment of clarity and realized that if their show kept running in place, it would suffer a slow, mediocre death. "Nurse Jackie" season 4 is all consequences, all the time — and is much, much more satisfying overall as a result.
 
How swift is the turnaround? The new season opens with Jackie checking into rehab, and within the first 30 seconds, we hear her drug counselor warn her, "Let's make this really clear: you're accountable now."
 
We quickly flash back to see how Jackie wound up in this place, physically and emotionally, about which I'll say little. But Brixius and Wallem are smart to recognize not only the need to shake things up, but the storytelling possibilities from all of Jackie's many secrets and the different people who could learn them. Not everyone knows everything (or, in the case of Facinelli's amusingly oblivious Dr. Coop, anything), but Jackie's various colleagues and loved ones start getting a look at different puzzle pieces, which puts the intensely private Jackie on the defensive and changes the nature of many of her relationships. If you feel like you've seen every possible interaction between, for instance, Jackie and temperamental opposite Zoey (Wever, hilarious as always), you haven't.
 
And it's not like the show does a 180 with Jackie. She may be trying to change, but her circumstances have changed far more than she has. She still has all of her flaws; she's just more conscious of them than before, and now has to operate in a world where others — including people who hold power over her future — are more aware of them, too. That feels real, and gives the writers and Falco a lot to work with.
 
And correcting the series' major flaw makes the quality of the rest of it even easier to see. Whatever issues I had with Jackie skating out of trouble, Falco has always been superb. If anything, Jackie's new status quo gives her more of an opportunity to play comedy, which she's done so well in the past on both this show and "The Sopranos." When Falco won a comedy actress Emmy for this role in 2010, she said, self-effacingly, "This is the most ridiculous thing that has ever, ever happened in the history of this lovely awards show. I'm not funny!" If she wins another one down the line, people who watch this show won't buy that from her.
 
And the series has become a very sturdy workplace comedy around Falco, one that also gets a shakeup with the arrival of Bobby Cannavale as Michael Cruz, a doctor representing the conglomerate that's purchased All Saints Hospital and intends to maximize its profits. Cruz allows the show to delve more deeply into our dysfunctional healthcare system, but he's not a cartoon villain, and the presence of an authority figure who has no allegiance to Jackie at this very vulnerable time in her life only ups the stakes.
 
Generally, when a show gets to the age "Nurse Jackie" is at, it's decided what it wants to be and sticks to that for as long as it can, for good or for ill. Every now and then, though, an older show can learn new tricks, and I was glad to see this one do it.