An exhilarating tale about a woman discovering her full potential and running with it, “Erin Brockovich” is everything that “inspirational” true-life stories should be and rarely are. Vibrant and often quite funny in its account of how an unschooled, twice-divorced mother of three spearheads an investigation that leads to the largest payoff ever made in a direct-action lawsuit, this very satisfying picture takes Julia Roberts into more realistic performance territory than usual and should lead director Steven Soderbergh into an uncustomarily rarefied commercial realm. R rating and fact that this is not a pure escapist confection like most of the actress’s films will undoubtedly result in somewhat lower than normal B.O. for Hollywood’s biggest female star, but there is still more than enough heart and humor here to put “Erin” in the winner’s circle, where the heroine ended up in life.

At the moment, Soderbergh is...