"Jack the Giant Slayer" is a capable, oft-wondrous fantasy-adventure tale—uneven, to be sure, but also largely crowd-pleasing as it goes for broke in the thrilling third act. With that out of the way, a few observations must be discussed. First of all, what is the meaning of the revisionist title when "Jack and the Beanstalk" would have aptly made more sense? The hero of the story, 18-year-old farmhand Jack (Nicholas Hoult), is neither oversized himself nor a slayer of giants. It may be true that, by film's end, he has had to kill to save himself and his fair maiden, Princess Isabelle (Eleanor Tomlinson), but it's not like he ever sets out to do away with giants and, as far as one can tell, he has no sociopathic tendencies. A second, more ironic, note: for a motion picture where the namesake giants are supposed to be its bread and butter, they are far and away the most uninteresting of all the characters, CGI creations through and through with few defining attributes and not for a second believable as live-action figures existing in the same space as their normal-sized counterparts. Is technology and cinema magic still not quite up to the appropriate capabilities, or does the bigger problem fall upon screenwriters Darren Lemke (2010's "Shrek Forever After"), Christopher McQuarrie (2012's "Jack Reacher"), and Dan Studney, who have conceived of their makeshift "bad guys" as mumbling, bumbling thugs lacking in dynamism and personality?

As a child, Jack loved for his farmer father to read him bedtime stories about the mythical giants who once wished to rule the earth until they were condemned to their own land high up in the sky. Ten years later, an orphaned Jack now lives with his uncle (Christopher Fairbank)—his father, it is mentioned, fell victim to the plague—the two of them barely scraping by. Sent into town to barter livestock, Jack ends up defending the beautiful Isabelle, princess of Cloister, and is subsequently handed some beans by a monk. "Whatever you do, don't get them wet," he is told. Faster than you can say Mogwai, a rainstorm blows through, saturating one of the beans just as Isabelle has arrived at Jack's door, having run away from the castle over an arranged marriage to crooked Lord Roderick (Stanley Tucci) that she wants no part of. From out of the bean grows a giant beanstalk, lifting the house—and the princess—up above the clouds. With valiant guard to King Brahmwell (Ian McShane), Elmont (Ewan McGregor), by his side, Jack agrees to lead an expedition up the beanstalk and into the territory of the giants to save Isabelle. Meanwhile, Roderick has much more devious plans, hoping to use the magical crown that controls the giants to overthrow the king and take down Cloister.

Until a large-scale, arrows-firing, drawbridge-collapsing climactic battle sequence, the giants in "Jack the Giant Slayer" are dull buffoons, with a conjoined duo leading the charge who play like a cross between a distaff Gollum and Jar-Jar Binks at his most unctuous. The true star of the piece beyond a sincere and earnest Nicholas Hoult (2013's "Warm Bodies") and a fetching Eleanor Tomlinson (2010's "Alice in Wonderland"), as Jack and Isabelle, is the leafy green beanstalk itself, an utterly rapturous visual effect that sends most of its ensemble perilously high into the sky. Not simply achieved in a quick climbing montage, getting to the top of the beanstalk is portrayed as a rightfully arduous and death-defying task, the ensuing set-piece to go along with it both legitimately hair-raising and appropriately magical. From there, the conception of the giants' world—what looks like an island floating in mid-air, designed with such detail and flourish there must be a brilliant architect amongst the inhabitants—is impressive, if not explored nearly enough to prove fully satisfying. Then again, Jack, Elmont, and a quickly rescued Isabelle aren't exactly given much to do, either, the story so thin in the middle section that all there really is left to accomplish is to turn around and make it back down to ground level in one piece.

Nicholas Hoult and Eleanor Tomlinson are well-positioned as love interests Jack and Isabelle, from starkly different sides of the track but unable to deny the cosmic forces drawing them together. As Elmont, Ewan McGregor (2012's "The Impossible") is underwritten and underutilized—a shame, because he's otherwise ideal for the part. Tastily surveying the role of dastardly Lord Roderick without turning him into a caricature, Stanley Tucci (2012's "The Hunger Games") is a terrific human foil for the protagonists, altogether more interesting than the giants. And, as King Brahmwell, Ian McShane (2012's "Snow White and the Huntsman") is commandingly regal, nearly setting his own precious daughter up for a miserable life before learning the error of his ways and the importance of her feelings.

If "Jack the Giant Slayer" is a hit-and-miss affair for a long while, a collision of grandeur, convention and bloat, director Bryan Singer (2008's "Valkyrie") pulls out his MVP card in time for a last half-hour that's easily one of the most involving, impressively cohesive battle sequences seen since 2003's "The Lord of the Rings: The Return of the King." It turns a mildly arresting, intermittently ho-hum intended blockbuster into one that's worth checking out, the level of technical artistry and showmanship on display quickly breaking down the viewer's defenses. Topped by a clever little zinger of a last scene, the film ends up being a fun action romp after all—and, again, that's in spite of the fantastical creatures of the title falling flat, both as characters and as blatant computer effects. With all the other elements working as well as they do, however, that's a trade-off that can be lived with.