After teaming up for the understated Cold War drama Bridge of Spies, director Steven Spielberg and actor Mark Rylance join forces once again for a very different kind of movie. The BFG, a fantasy film based on a children's story by Roald Dahl (author of Charlie and the Chocolate Factory and The Fantastic Mr. Fox), centers on a precocious orphan named Sophie (Ruby Barnhill) who spots something truly unbelievable in the middle of the night: a giant creature (played by Rylance with the help of some special effects) who quickly snatches the little girl from her bed in order to keep his existence a secret.While he might seem like a force to be reckoned with in the human world, Rylance's vegetarian leviathan -- called "the BFG" for "the big friendly giant" -- is constantly picked on and teased by the larger, meat-eating members of his race in his home country. As Sophie joins the BFG on his travels, the pair have some traumatic run-ins with giant, dim-witted bullies with names like Bloodbottler and Fleshlumpeater (played by versatile comedians Bill Hader and Jemaine Clement, respectively). When the other behemoths begin to take children from their beds for the purpose of eating them, Sophie gets the BFG to control the Queen of England's dreams (a special talent of his) in order to prompt her, and the military forces of the Crown, into action.For readers who don't find that plot description fanciful enough, Spielberg and his creative team have also brought to vivid life the city streets of England at dusk, a dreamscape full of orbs that represent our nighttime visions, and the secluded land of the giants. As for the human components of the story, the heavy lifting falls on the shoulders of Rylance and relative newcomer Barnhill (whose only previous acting credit was a recurring role on the British TV series 4 O'Clock Club). In a charming, wide-eyed performance reminiscent of Mara Wilson's turn in Matilda (another Dahl adaptation), Barnhill manages to imbue her character with a great deal of wit and wonder. Viewers are able to go on a hero's journey along with Sophie, watching as her independent streak crystallizes into a sense of leadership and she evolves from a victim of circumstance to the person driving the plot forward.Much less surprising is Rylance's terrific performance as the title character, which is equal parts heartwarming and devastating. The CGI necessary to animate the BFG can't mask the British theatre veteran's gift for conveying a tremendous amount of emotion in a single facial expression. The movie mostly succeeds in translating this highly imaginative yarn to the big screen, as it skillfully traces Sophie's journey from her orphanage to a behemoth's lair to the Queen's abode. However, the film becomes a little too breezy just as it should be ramping up for a thrilling climax. Spielberg weirdly packs most of the big emotional moments into the first half of the story, which means that there's little sense of catharsis at the end since the BFG has already confronted his demons. Essentially, the movie builds toward a treacly letdown rather than a genuine emotional release.While the narrative peters out at an inopportune moment, Rylance and Barnhill remain capable guides through a fantastic world that represents our everyday obstacles and fears. Aimed squarely at the heartstrings and imaginations of young viewers, The BFG mostly hits the mark as a touching and visually appealing experience.