Since his Oscar-winning breakthrough with “Good Will Hunting,” Ben Affleck has become firmly entrenched in the Hollywood mainstream. He’s starred in countless big-budget movies—including “Armageddon,” “Reindeer Games,” “Daredevil” and “Gigli”—yet seemed to lose more and more critical clout with each successive project.

Now, however, Affleck is on the comeback trail. He’s rehabilitated his image in the tabloids—partly by marrying and having a daughter with Jennifer Garner in 2005—and last year he earned rave reviews, a Golden Globe nomination and a Venice film festival best actor award for his portrayal of the late George Reeves in “Hollywoodland.”

For his latest project, “Gone Baby Gone,” Affleck stays behind the cameras, writing and making his directorial debut with the adaptation of a popular novel of the same name by Dennis Lehane (who also wrote “Mystic River”). He leaves the acting duties to a strong cast that includes Ed Harris, Morgan Freeman, Michelle Monaghan and his brother Casey Affleck, who stars as a Boston detective embroiled in a kidnapping case filled with lies, deception and brutal moral dilemmas.

Metromix caught up with the elder Affleck recently, who spilled the beans on picking this project, casting Casey and changing the trajectory of his career.

Initially you were going to write and possibly act in “Gone Baby Gone.” How did you decide it would be your directorial debut?
The script took a long time. Ultimately it got to the place where I sort of liked it, and then at that point I was starting to feel maybe I was ready to direct something. Also, I had really started to fall in love with this piece of material. I really understood the world it was set in. I came from this city.

How familiar were you with the seedier side of Boston, where most of the film takes place?
I’d like to think not all that familiar. I think I was familiar with the accent, culture and world-view, a certain element of parochialism. In a weird way, that’s one of the more appealing aspects of Boston because it distinguishes it from a lot of the rest of the country, which has become really homogenous, where it’s just another Banana Republic or TCBY. The whole country is just so chained out. Boston still has an insularity to it, a specificity that’s unmistakable. But this movie does have a level of darkness that wasn’t second nature to me. It required research, and it just meant that we had to walk into a lot of dark places and find folks to be in our movie.

Are you concerned at all that people might compare your movie with “Mystic River,” since they’re both based on books by the same author?
Clint Eastwood is one of my heroes. This movie openly aspires to be “Mystic River.” That is a spectacular movie. I think in a weird way it kind of helps, because [Eastwood] made such a good movie from a Dennis Lehane book set in Boston, so that’s probably a pretty good advertisement, you know? It says, like, “Hey, look! This was already a great movie set in Boston from a Dennis Lehane book.”

The lead role of detective Patrick Kenzie was initially written older, as a guy in his late thirties. What made you change that, and did you always have your younger brother, Casey, in mind for the part?
When I originally looked at [the character], I had a hard time getting excited about that. And when I reconceived [Kenzie] as being 29, it seemed more exciting story wise, because the guy has more to lose and the stakes are higher. You go through a trauma at 40 it hurts you, but it doesn’t change your life. It really forks the road of your life when you’re still in your late twenties. And not only that, but all of a sudden I had available to me, at that age, a spectacular actor who understood Boston, who I really had a shorthand with, who I knew I could get and who we could afford!

It looks like the decision paid off. What do you think of the attention he’s been getting for his one-two punch with roles in your movie and “The Assassination of Jesse James”?
I think it’s spectacular. It’s satisfying to see somebody who has labored a long time to finally get their due. And I’ve seen up close in Casey a guy who is so talented, who keeps on not getting his break, finally getting the opportunity to be in these movies and getting a chance to prove himself. That’s really rewarding even if he wasn’t related to me…

You won an Oscar for co-writing “Good Will Hunting.” What took you so long to get back to writing and having such a hands-on role in putting together a film?
I think part of it was wanting to change what I was doing. I used to kind of make choices based on what I anticipated other people would find interesting or what would appeal in terms of a mass audience. Basically, I got to a point in my life where I reexamined why I was doing what I was doing and ultimately decided that, you know, the only person I could really trust as a barometer was myself. So if I was going to succeed or fail, I was going to succeed or fail on the basis of my own instincts, rather than try and kind of pander to some imaginary audience.

So, does your instinct suggest more movies as a director?
Yes. I’ve really kind of fallen in love with the process of doing this stuff. It’s really exciting, it’s really scary and there was a part of every day where I felt like I had NO idea what I was doing. But then, at least at some point in the process, I found it exhilarating and satisfying in a way that’s just very rare for me. So that’s something that I want to keep going after.