A roiling visual extrusion rendered from computer-generated imagery, Jack the Giant Slayer makes you long for the days of Ray Harryhausen.
With his sometimes jerky stop-motion animation that was state-of-the-art movie magic for decades, Harryhausen somehow convinced you more thoroughly that his characters were alive and had feelings and thoughts than anything Bryan Singer comes up with using a warehouse full of mainframes in Jack.
You barely care about most of the live characters, let alone the CG ones. The action is never captivating or even very convincing. And the story is mostly an excuse for outsized action setpieces -- and there's very little that's magical about those.
Adapted from a couple of different fairy tales into this fantasy-action-adventure by a quartet of writers, Jack the Giant Slayer is set in a medieval time when people apparently coexisted with giants, who live in a land in the sky accessible only by the occasional magic beanstalk. But the risk/reward ratio for planting the beans that produce a ladder to the clouds is pretty high, riskwise, given that the giants use the beanstalk to visit the land below and eat the humans. Needless to say, those beans are kept locked away.
Jack (Nicholas Hoult) is an orphan, living with his uncle, tasked with selling the family horse and cart to help keep the farm alive. Instead, he gets cheated out of the horse by a monk, who gives him those famous magic beans, which he's trying to keep away from someone with evil intent.
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