On the day we meet - in the cosy lobby of New York's Bowery Hotel - he appears as earnest and goofy as he does on screen.
But Braff, being Braff, is now riding the wave of a new controversy. Determined to bring Wish I Was Here to fruition, but unable to secure conventional studio backing, last April he appealed to the users of crowd-funding site Kickstarter for assistance. In a specially made video he said he wanted to make an unofficial sequel to Garden State, without, as he put it, "the money guys".
The reaction was extreme. Many wondered - in savage terms - why anyone should donate money to a wealthy celebrity to fund his own vanity project.
"Rich person Zach Braff wants the internet to pay for his next movie," reported US website Gawker.
App users: Tap here to watch the trailer for Wish I Was Here.
But Braff, 39, sees it differently.
"It was about fighting for artistic integrity," he says. "It wasn't a money-making scheme. If I want to make money I'd go do a network TV show. This experiment, which was a tremendous success, was [to find out] what it would be like if you took all the corporate involvement out of the process and you made a movie with - and for - your fans. Some people will love it, some won't, but most importantly, you'll make something with and for your fans."
The irony of the vitriol was that it helped the project. As he explains: "The detractors were driving more traffic to the campaign than anyone else. The CEO of Kickstarter said I drove more traffic to their site in one day than anyone ever had." The project attracted 47,000 backers, donating anything from $10 to $10,000, allowing it to reach its $2 million target in just three days. (Braff also spent millions of his own money on the film.) I tell him I was shocked at just how cross it got people.
"That's a good paragraph starter!" He adopts a Mary Poppins-ish accent: "I sat down with Zach Braff in the Bowery hotel. I was surprised about how pissed off people got. Did I mention I f***ing love his movie?"'
Well, the expletive might be overstating it but Wish I Was Here did make me laugh. In it, Braff is an unemployed actor home-schooling his two children while struggling with questions of faith as he faces the terminal illness of his father, played by Mandy Patinkin (Saul Berenson in Homeland). There's a scene between Patinkin and Kate Hudson, who plays Braff's wife, that I found revelatory.
"Do you hear that?" he says, picking up my recording iPhone to speak into it. "Revelatory!" Replacing the phone, he adds: "I think that scene with her and Mandy is pretty special. I think it's one of the best things I've ever done."
As with Garden State, in which Portman played his potential salvation, Hudson's character is the person holding him together and the one, as he puts it, "who's going to call me out on my bullshit". "I have," he admits, "this fantasy of being rescued by some great strong woman."
If anything, the movie suffers from Braff's character being just too tediously likeable. His spontaneous feats of fatherly fun - test-driving a sports car with his kids, telling ghost stories to them around a campfire - seemed to me contrived. Didn't he want to make his character a bit darker or more complex?
"Well, he's pretty much an asshole at the beginning, I think," he says, bristling a little. "He's a narcissist who's checked out from his family. He's annoyed by his kids, he's ignoring them, he's annoyed that they're in the very faith that he's indirectly imposed upon them."
Braff and his brother, with whom he wrote the film, were raised in the Jewish faith but as a teen Braff had what he calls "an epiphanous moment" when he realised that "people really thought there was a Noah's Ark and a Garden of Eden", as opposed to seeing them as "beautiful allegories".
He adds: "I saw a list of countries and the United States was second-to-last in believing in evolution. The fact that science is called into question now made me even more passionate about wanting to talk about this. It isn't until your 30s that you go, 'God, what the hell do I believe? What do we teach our children? What are we doing here?'"
For those who know Braff only as the hapless junior doctor JD in the very silly medical comedy Scrubs, it may be surprising to know these are the sorts of questions occupying him so passionately. The TV series was his big break, a role that made him famous virtually overnight. Just before he was cast, his acting career was close to non-existent. He had had a bit part as Woody Allen and Diane Keaton's son in Manhattan Murder Mystery, but by 2001 "I was working as a waiter. I made about 1000 bucks. My parents gave me $5000 and I put it all into buying a Nissan 240 SX. I loved that car."
Zach Braff and Kate Hudson.
Braff is the sort of person to make you want to believe in karmic power - specifically, to wonder whether that gift was cosmically repaid years later when a wealthy businessman, "a fairy godfather", effectively funded Garden State. "And then," says Braff, "I went to [the film festival] Sundance and won the top prize, other than an Oscar, that a film-maker could make, which is the Independent Spirit Award for first feature. So all these magical things happened, and because I then didn't want to go get on the conveyor belt and make romantic comedies for a studio, I ... hit a brick wall. So when I stumble across [Garden State] on cable, it makes me melancholic. And I never said that it was the voice of a generation or any of that bull.
"The entire media system," he adds, "is designed to build someone up and then tear them down."
He talks a little about how great movies of the past (he cites Annie Hall) wouldn't get made in the hyper money-conscious climate of corporate Hollywood.
Nevertheless, he tells me he has no intention of crowd-funding a project again. Being forced into the role of "the person who was going to educate Earth on the intricacies of film finance, the intricacies of crowd-funding" was just too exhausting.
Then, acknowledging the gloomy turn the conversation has taken, he makes a sad trombone noise: "wah-wah-wahhhhh".
"We need to end on something uplifting!" he says. He thinks for a moment. Then tells me: "You have approximately 60 summers left. So you need to make the most of those. You shouldn't be talking to me in a dark hotel lobby, you should be out walking a puppy." Which - as sweethearted as it is insufferable - is as Braff-ish a valediction as I can imagine.
Who: Zach Braff, actor writer and director
What: Wish I Was Here also starring Kate Hudson and Mandy Patinkin
When: Opens at Cinemas on Thursday
