IN SHERRYBABY, actress Maggie Gyllenhaal is stripped bare - emotionally and literally. It is a raw and vulnerable performance, the kind of role that works only when the actress in question is able to lose herself inside the character. She plays a recovering heroin addict who, in a sense, is looking for salvation. The film opens as Sherry, after a three-year prison term, sets out on a journey to stay off drugs and reclaim the love and trust of her young daughter, whom she missed desperately.

While US critics were divided over the film itself, there has been high praise for Gyllenhaal, some suggesting Sherrybaby is the strongest example to date of why the 28-year-old has become one of the most important actresses of her generation, and tipping her for an Oscar. This would seem to be her moment, Sherrybaby being one of four new films that show her multicoloured versatility. She also plays a pastry chef in Stranger Than Fiction, a worried wife in World Trade Center and a children's book author in Trust the Man. "She has a sparkling mind, a wealth of emotion, and miles and miles of charisma," says Laurie Collyer, who wrote and directed Sherrybaby. "She has the ability to turn the darkest, most difficult characters into someone you would want to know."

Gyllenhaal is taking it in with a Zen-like calm. "Most of the projects that I've ended up being very proud of have involved a certain amount of intuition, like there was something in the character that I had to work through," she says, resting on a couch at the Château Marmont on a humid afternoon. "At the time, it's not particularly an intellectual or rational choice. It comes from somewhere else, maybe something more unconscious. That's true of all of these movies that are coming out."

She grew up understanding the power of acting. Her father is director Stephen Gyllenhaal (Losing Isaiah). Her mother is screenwriter Naomi Foner (Running on Empty and last year's Bee Season). Her brother is, of course, Jake, who commanded the spotlight last year after Brokeback Mountain. Acting always felt like stepping into a "deep daydream", she says. "It was always a pleasure. It was fun for me."

After graduating from Columbia University in 1998, Gyllenhaal started auditioning, earning small parts in a few films. Then, in 2002, she scored a lead role in the indie movie Secretary, earning her dizzying critical acclaim, including a Golden Globe nomination for her portrayal of a quirky young woman who embarks on an obsessive sadomasochistic relationship with her older boss (played by James Spader). More than a dozen films have followed. In Sherrybaby Gyllenhaal uses her body and her sexuality to navigate a world in which she finds herself without money or credibility. The role, she said, was soul-wrenching.

"I really got sucked into Sherry in every way," she says. "Sherry has this kind of naiveté, this fierce hopefulness. Every time an obstacle comes at her, it's doubly sad. She can't afford even a second of acknowledging how lost and painful her life is."

Gyllenhaal says it took her weeks after the film was completed to let go of the part. "I really had a hard time. There was all this stored pain, Sherry's pain, in my body. It started coming out in all sorts of ways, in my skin, I was smoking. I remember going to a beautiful wedding in Spain afterward and I was just a mess. I wasn't myself." Although she has since moved on (she forced herself to stop smoking), she says that watching the film is still not easy. "I feel so much more exposed watching it than I did making it."

In the movie, she gives an honest portrayal of an addict who struggles to be a good mother while dealing with her own childhood pain. Sexually exploited by men, she also exploits them. When the movie premiered at the Sundance film festival earlier this year, she considered walking out of the cinema. "That's never happened to me before." She felt naked - in every sense of the word. "In retrospect, I'm proud of having made the movie," she says. "It's a compassionate movie about someone who is so easy to dismiss, so easy to judge. We tried with everything we had not to judge her. That's how I would like to be in the world."

After the heaviness of Sherrybaby, Gyllenhaal says, she found it refreshing to make two romantic comedies, Trust the Man and Stranger Than Fiction "It ended up being a total pleasure."

In Stranger Than Fiction, Gyllenhaal plays a tattooed pastry chef who becomes the love interest of an immigration agent played by Will Ferrell. "It was nice to play someone healthy," Gyllenhaal says. "She gets disappointed. She gets hurt, but she isn't going through any tragedy. I loved being her." The part also came with an added benefit: Gyllenhaal took baking classes from Nancy Silverton, founder of La Brea Bakery, to prepare for the part. "We were baking five things at once." Her pastry creations made their way home to her actor fiancé, Peter Sarsgaard.

The levity didn't last long, however. Gyllenhaal spent last autumn working on World Trade Center, playing the wife of Will Jimeno, a Port Authority police officer pulled from the rubble. Gyllenhaal says she loved working with director Oliver Stone, but the drawn-out production schedule and the subject matter meant the project was a difficult one. "We would have a couple of weeks of hard work and then a month off," she says. "It sort of felt like taking a Band-Aid off slowly." As for delving into 11 September, Gyllenhaal says: "There was so much more pain than I anticipated, and there was almost no catharsis."

When we meet, she is heavily pregnant, and says it feels good just to relax and enjoy the approach of motherhood. "I can't anticipate what it will be like to be a mother" she says, taking a sip of ice water. "I'm just going to focus on that for a while."

• Release dates: Trust the Man is out now, World Trade Center is released on 29 September; Stranger Than Fiction is out on 1 December; Sherrybaby's UK release date is still to be confirmed.

IN HOLLYWOOD, everyone seems to be baring all this autumn - not just Maggie Gyllenhaal. Going au naturale in a cinema near you now is Jason Statham, in action flick Crank. "It was a little unnerving," the British actor admits, "because there were 200 people looking at my pasty white bum. I said, 'Oh my God, what am I doing?'."

The Last Kiss The comedy-drama by Academy Award-winner Paul Haggis (Crash) showcases several cast members as they shed their clothing in explicit love scenes involving, among others, Scrubs star Zach Braff and OC vixen Rachel Bilson.

The Last King of Scotland This drama about infamous Ugandan dictator Idi Amin (played by Forest Whitaker) includes a graphic love scene between Amin's Scottish physician (James McAvoy) and one of Amin's wives (Kerry Washington).

Shortbus John Cameron Mitchell's comedy drama about New Yorkers who visit an art/sex salon where anything goes. Sex is at the centre of their search for connection, and though the film's sensibility is more art house than porn house, some critics have called the production pornographic.

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