With the number of rom coms in decline and comic book movies hitting nearly as often as they miss, there's not a more tiresome Hollywood trend right now than this insistence on re-imagining every classic fairy tale as live-action adventure films. We've seen "Alice in Wonderland", "Snow White", "Hansel & Gretel" and "Little Red Riding Hood" become exercises in bloated mediocrity, and now "Jack and the Beanstalk" can join the list.

Of these adaptations, Bryan Singer's Jack and the Giant Slayer is one of the more tolerable, a middling microcosm for the sub-genre with some memorable characters and moments and some that are equally grating.

Nicholas Hoult stars as Jack, a farmboy who unwittingly comes in to possession of magic beans that, when wet, sprout as gargantuan beanstalks that connect the human world with the realm of bloodthirsty man-eating giants. When the beanstalks hurtle skyward, Jack gets entangled in royal intrigue, going up the stalk to rescue Princess Isabelle (Eleanor Tomlinson) from the giants and from her traitorous husband-to-be Roderick (Stanley Tucci) and, upon coming back down, helping to defend the Kingdom of Cloister from the enormous threat hot on their heels.

The budding, forbidden romance between Hoult and Tomlinson was, to my surprise, the highlight of the film. As in Warm Bodies, Hoult displays a second-rate charm that might not sustain a long career, but certainly works for the time being. Only he and Tomlinson, along with Ewan McGregor as Elmont, commander of the king's elite guards, commit fully to their roles, providing just enough of a spark to carry the audience through all 114 minutes.

You'll need every ounce of the energy the trio have to offer because most of the film's other elements weigh it down. The primary villain changes with jittery frequency, from Tucci's Roderick to Fallon, the two-headed leader of the giants voiced by Bill Nighy and John Kassir, to a quartet of rival giants, Fe, Fi, Fo and Fum. None of them are even remotely compelling, the CGI giants lacking some visual punch and Tucci cartoonishly and uncharacteristically poor as the only human baddie. On the flip side, Ian McShane turns in a flat performance as Isabelle's father, King Brahmwell. (It's hard not to wonder if things might have worked better had McShane and Tucci switched roles).

For long stretches Jack the Giant Slayer is entertaining, and for similarly long stretches it's almost unwatchable. It's something to do, I guess, which seems to be the depressing operating principle behind every other fairy tale adaptation like it so far.