A downbeat, worthy drama, Monster sees Charlize Theron transform herself from B-movie actress to Oscar-winning star. Although that doesn't mean this based-on-fact film is especially noteworthy, aside from how she has altered her appearance - gaining weight and using artificial teeth to look suitably sour-faced as real-life abuse victim and prostitute-turned-serial killer Aileen Wuornos. It's a striking change from Theron's usual glamorous roles - and there's more to it than mere make-up - even if the film doesn't offer much in the way of insight or surprise in what is a very straightforward story.

Wuornos - who was executed in 2002 after ten years on Death Row - was hyped in America as the world's first female serial killer. But Monster, to the credit of writer-director Patty Jenkins, attempts to explore the person behind the headlines.

A virtually life-long prostitute, 'Lee' is presented here as a broken woman desperate for a normal life with her new lesbian lover. Seeking to support Sel (Christina Ricci), she carries on hooking - but when a client rapes and threatens to kill her, she shoots him in self-defence. Then she decides the next 'john' deserves to die. And the next. And the next...

"PREDICTABLY TRAGIC, TRAGICALLY PREDICTABLE"

Shunning sensationalism, Jenkins doesn't judge Wuornos. The kill scenes are neither shocking or exciting: just there, for us to consider Aileen's actions. The highest moment of emotion comes when she's deciding whether to shoot a bloke who's trying to help, rather than hump, her. This is probably because it is the film's sole moment of uncertainty: everything else plays out exactly as you expect - predictably tragic and, in filmmaking terms, tragically predictable.

Theron offers a tender performance of fractured humanity, while Ricci - in the less showy role - also impresses, capturing a callow, selfish character who manipulates the older woman, selling her a dream of love. But another angle on the same story - perhaps told from Wuornos' Death Row wait, or touching on her abuse-filled background - might have been more compelling. Instead, Monster is measured but somewhat monotonous: a film, like its complex title character, executed with depressing efficiency.