The premise was fine (15th generation "Jack Robinson" learns the old story is true and undoes the harm caused by the original Jack, removing the curse from his family). The cinematography design is okay, and the fantasy lands reasonably well constructed.
However, the script is pathetic, with enough plot holes to double as Swiss cheese, big enough for giants to walk through, especially toward the end. The writers couldn't decide if they were doing comedy or not, and ended up mostly with "not" (barring a few mildly humorous moments)
Prime material for the "How It Should Have Ended" internet site.
The dialogue is inferior to Saturday morning cartoons, and the music is a joke.
It might possibly entertain a desperate pre-teen, but I wouldn't subject my own kids to the inanity for fear it would rub off.

SPOILERS for the benefit of would-be playwrights:

(2) The basic story is okay, although no explanation is given for the announcement that the Robinson family was cursed by what Jack-1 did, or why Jack-15 was the only one who could end it.
(2) The girl Ondine from the Giant's Land travels to Earth with "magic" devices, and the God-entities introduced at the end of the show to judge and condemn Jack appear without even needing those, but no explanation is given as to why none of them followed Jack-1 to reclaim the goose and the harp at the very beginning.
(3) The God-entities were superfluous, unneeded, and pathetic.
(4) Although the story takes place exclusively in England (to all appearances), two major characters have East European accents, even though one of them began the movie with an English voice. (I think it was filmed in EE). (And the other one is played by an American actor.)
(5) The time shift of 1 day in Giant-land = 1 year on Earth is invoked only when convenient. No one explains how Jack's mother acquired a giant beanstalk that no one noticed for several months or years before Jack returned (time unpecified, but long enough for Ondine to fall in love, sort of).
Not to mention hacking up and burying a giant without anyone noticing.
(6) Jack's workers uncover the giant's bones which are re-strung and displayed at the castle, including during a massive building project that ends in a public casino ballroom, and are analyzed by a team of scientists, but no one tells the press. Um, I don't think so.
(7) Ondine caused all the trouble in the first place, but no one upbraids or judges her; in fact, she gets sympathy from the dead giant's son.
(8) Ondine doesn't know Jack-15 any longer than Jack-1 but she "falls in love" with him too, and trusts him (justified this time, but how would she know?), and why didn't she come for the goose and harp any sooner?
(9) The goose is just plain annoying, and not even successful as a comic relief.
(10) I could probably think of other things, but this is enough. ( )