'Alita: Battle Angel'

What happens when a famously seat-of-the-pants director goes to work for a notoriously detail-oriented filmmaker? Unsurprisingly, in the case of “Alita: Battle Angel,” a big mess, though an exhilarating one.

Robert Rodriguez, he of “Sin City” and “Spy Kids,” is the director in question. “Titanic” and “Avatar” auteur James Cameron is his boss — and co-screenwriter, along with Rodriguez and Laeta Kalogridis (“Terminator Genisys”) — in adapting Yukito Kishiro’s cult-fave manga “Gunnm.” Together, they conjure up exciting action sequences in a meticulous steampunk landscape, centered on a performance-capture CGI character that’s the closest Hollywood has come to the edge of the “uncanny valley.”

It’s the year 2563, some 300 years after a great war that left humanity divided into two worlds: The city in the sky Zalem, and the grungy, bustling areas on the surface, like Iron City, where Dr. Dyson Ido (Christoph Waltz) repairs workers’ cyborg parts and scrounges for supplies in the mounds where Zalem dumps its refuse.

Ido’s latest salvage item is the head and shoulders of a female cyborg that contains a fully intact brain of a human female, a teen-ager. Ido cleans up the cyborg parts, and provides a new body — the origins of which form the basis of Ido’s backstory, and his connection to a shrewd rival doctor, Chiren (Jennifer Connelly). Ido gives his new creation the name Alita, and raises her like his own daughter, though they both have to solve one mystery: Akita’s identity and memory of her life in Zalem.

Alita looks like a normal teen girl, except for her enormous eyes, which take in her surroundings with a measure of curiosity and innocence. The eyes are evocative of Japanese anime style, but also have the haunted look of a Margaret Keane painting — and that mix of emotions is how Rosa Salazar, who deftly provides the voice and body performance to Alita, plays the character.

Alita discovers a lot about her self and her new world, through Ido and Hugo (Keean Johnson), who befriends Alita on the street, teaching her about the taste of chocolate and the popularity of motorball — a combination of roller derby and Rock’em Sock’em Robots that is the only chance anyone in Iron City has of getting up to Zalem.

Alita also learns there are nasty bounty hunters, called hunter warriors, who capture wayward cyborgs at the demand of The Factory, which provides raw materials for Zalem. Alita is surprised to learn that Ido is a hunter warrior, using the bounties to pay for repairs of his Iron City clients. Alita finds that she has fighting skills, which spring into action when a brute cyborg, Grewishka, is sent to kill her — under the orders of Nova, the unseen leader of Zalem, working through Vector (Mahershala Ali), the gangster who controls Iron City’s motorball arena.

Rodriguez and his team cram a lot of world-building into two hours, and if that means a bare framework of a plot, then so be it. It’s the rust-speckled wonders of Iron City that Rodriguez and Cameron are most interested in, along with the spunky CGI warrior in the middle of it all. Maybe if there are future “Alita” adventures — and the movie’s ending sets up franchise possibilities — we’ll get a complex story to fully inhabit this fascinating world.

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‘Aiita: Battle Angel’

★★★

Opens Thursday, February 14, in theaters everywhere. Rated PG-13 for for sequences of sci-fi violence and action, and for some language.  Running time: 122 minutes.