CONTAINS SOME SPOILERS, INCLUDING DISCUSSION OF THE ENDING (BECAUSE IT'S KIND OF IMPORTANT WITH REGARD TO WHAT'S WRONG WITH THE MOVIE)
The more important of the two names on the poster for this new Canadian/Spanish horror movie isn't star Jessica Chastain (unrecognisable from Zero Dark Thirty), but Guillermo Del Toro. He didn't direct or write it (that's down to Andy Muschietti, who'd already made a short of the same name in 2008), but he's billed as executive producer, whatever that might mean, and the credits actually begin with "Guillermo Del Toro Presents". And there's a familiar GDT feel about the film: children, insects, fairy stories and sheer horror that's most reminiscent of the great Pan's Labyrinth as well as the solid Don't Be Afraid Of The Dark (which he co-wrote and produced).
Following a financial collapse, a distraught Jeffrey (Nikolaj Coster-Waldau) abducts his young daughters and heads out of town. But the car crashes and they end up wandering the wintry forests until chancing upon an isolated cabin - home to someone or something which they refer to as Mama. Five years later the girls are found, but when they're taken into care with their artist uncle Lucas (also Coster-Waldau) and his rock chick girlfriend Annabel (Chastain), Mama isn't about to let them go... Can they figure out who or what she is, or was, and stop her before she reclaims the girls forever?
Probably the less you know the better. Mama herself is a persuasively effective horror bogey(wo)man, single-minded in what she wants and ruthless in securing it. It's a pity that the film opts to reveal her through whizzy CGI which is undeniably spectacular but the full-on monster approach isn't nearly as unsettling as the first hour of subtler, creepy moments. Some of the jump moments work well (some work superbly - I had to look away from the screen on several occasions) but others seem cheap and unnecessary as Mama suddenly materialises where the characters don't see her, leaving you wondering why Mama would bother doing that.
Skip this paragraph if you don't want details of the ending, as that's the source of my other big problem with the film: the death of a child. I'm not happy with movies that kill the kid any more than many audiences are okay with movies that kill the dog, as it seems like a cheap taboo too far (see Hobo With A Shotgun) and, while it means the movie doesn't have a cosy and predictable Hollywood ending, it still leaves an odd taste. And since this ending does focus on the death of a child, this would surely leave Annabel and Lucas struggling to explain just what happened to the girl to social services, the police, the family courts etc. Even if the cause wasn't supernatural, it would be a hell of a difficult sequence of events and incidents to explain away.
By and large, though, Mama the movie is pretty good, anchored by strong performances (from Chastain and particularly the two girls) and with enough domestic chills of the Sinister and Insidious vein to keep it nicely unsettling for the most part (aided by lots of low brass rumbles in the Fernando Velazquez score). If it does drop the ball in the third act with too much digital effects work and an unsatisfying conclusion, there's still enough good stuff in the first hour or more to make Mama worth seeing.