I know Julia Roberts is a huge movie star, but who knew she could act? She’s ruled the box office for the last 10 years since her breakout performance in "Pretty Woman," but never wowed me until her recent turn in "Erin Brockovich." Roberts is a revelation as a feisty single mom taking on the establishment in the latest movie from gifted director Steven Soderbergh ("Out of Sight" and "The Limey"). She has always been very skilled at romantic comedies, most notably "My Best Friend’s Wedding" and "Notting Hill," but lacked the emotional depth and maturity to carry a successful drama. Her character in "Erin Brockovich" is everything her previous dramatic roles were not. Roberts has delivered a passionate, smart and funny performance, which is easily the best work of her career.

Unlike her earlier attempts, Roberts’ persona helps serve the storyline rather than detract from it.

A great deal of credit should go to Soderbergh and writer Susannah Grant (the upcoming "28 Days") for providing a role that was more than just a "star" vehicle. Erin Brockovich is a chain-smoking, foul-mouthed, twice-divorced, mother of three with a chip on her shoulder and attitude to spare. In many of her other films, Roberts has floated by on her natural charisma. She devoted nothing to her parts beyond a big smile and pretty hair. Soderbergh and Grant have helped Roberts develop a character where those qualities are put to good use, but they’re not the whole show. Unlike her earlier attempts, Roberts’ persona helps serve the storyline rather than detract from it.

Soderbergh focuses on Roberts’ strengths as an actress and surrounds her with an amazing supporting cast, including Albert Finney ("Miller’s Crossing"), Aaron Eckhart ("In the Company of Men") and Marg Helgenberger (TV’s "China Beach"). Finney is wonderful as her boss, a frazzled personal injury attorney. Roberts and Finney have great chemistry together as they assume a tempestuous mentor/student relationship. Eckhart is proving to be one of the more versatile actors working today. As Erin’s gentle biker boyfriend -- complete with long hair, tattoos and a scruffy beard -- he is unrecognizable from the corporate shark he played in "In the Company of Men" or his schlub husband from "Your Friends and Neighbors." His character is a nice guy without being a doormat, the fate usually suffered by actors in this type of role.

The movie begins with Erin’s luck going from bad to worse as she gets into a car accident following a failed job interview. When her attorney loses her personal injury lawsuit, she hounds him until he gives her a job. While sorting through paperwork on a pro bono case, Erin discovers that the plaintiffs are all suffering from health problems. She does a little more probing and learns most of the families in this particular town are dealing with ailments that could be related to pollutants from a nearby industrial plant. She identifies with her plaintiffs, who are working class parents just like her. With no legal experience or formal education, Erin sets out to prove that the careless corporation poisoned her clients.

The plot of this movie, which is based on a true story, is very similar to last year’s John Travolta legal drama "A Civil Action." While that movie focused on the lawyers and their courtroom sparrings, "Erin Brockovich" is more focused on the human elements of the story. The drama comes from Erin’s tireless efforts to uncover the truth. She cuts through all the red tape to remind the lawyers that it’s people’s lives -- and not dollars -- that are at stake. It’s fun to watch her go head-to-head with lawyers and other corporate lackeys. These scenes crackle with energy and humor.

Sometimes movies based on true stories can be bitter pills to swallow.

Legal dramas usually focus on the transformation achieved by the lead character through their work on the case. In "A Civil Action" for example, Travolta’s greedy ambulance chaser becomes an idealistic crusader. Roberts’ character undergoes an even more remarkable change. Her work on the case inspires her to achieve her true potential. She’s not only trying to make life better for her clients, but for herself and her children. Her success gives Erin her first real taste of self-respect and professional achievement. The major revelation in "Erin Brockovich" is not a legal victory, but how this woman’s steely determination turns her life around.

Sometimes movies based on true stories can be bitter pills to swallow. They make a statement, but forget to entertain their audience. "Erin Brockovich" has a message, but it places a higher priority on telling a good story. Soderbergh’s expert touch makes a tremendous difference with a film that could have degenerated into a movie-of-the-week in lesser hands. While it is lacking the jump cuts and flashforwards of "Out of Sight" or "The Limey," Soderbergh retains enough of his personality to give the film a pizzazz that’s missing from most docudramas.

Soderbergh and Grant also practice restraint in other ways. Many films mine drama from extreme situations like car chases, children in jeopardy, etc. "Erin Brockovich" takes the path less traveled by paying attention to smaller moments. There’s a marvelous scene where Erin is driving home from work late and calls her boyfriend on her cell phone. This happens after she has ruffled some pretty powerful feathers so I was expecting a car to force her off the road or start chasing her -- the typical Hollywood flash. Instead, you learn that Erin has missed her nine-month old daughter’s first words. As she starts to cry, you realize what this case is costing her. The scene surprises you and has a greater emotional impact than any car chase.

"Erin Brockovich" is a welcome respite from most of the junk that’s been unleashed on audiences since the beginning of the new year. It’s a compelling story of one woman’s personal and professional triumph, with moments of genuine emotion and sly humor. Nowadays when even legendary directors are making disappointing movies, Soderbergh delivers his third consecutive exceptional film. He has also achieved what no previous filmmaker ever could, which is guiding Julia Roberts to a winning dramatic performance. The only disappointing thing about this movie is that it didn’t come out early enough to be considered for this year’s Academy Awards. I’ll keep my fingers crossed for next year.