If imitation is indeed the sincerest form of flattery, then The 7th Voyage of Sinbad can confidently feel flattered. Jack the Giant Killer borrows not only the earlier film's leading man, but also its villain and director. It features several plot points that are eerily reminiscent, too. A genie in a lamp becomes a leprechaun in a bottle, for instance. Heck, they even manage to come up with a reason to set half the film at sea.
Finally, it features stop motion monsters that are, shall we say, heavily inspired by Ray Harryhausen's cyclops from that film. Heavily inspired.
Left: this film. Right: Sinbad's cyclops.
Even with the small images above, you'll probably notice immediately that the stop motion work in this film isn't as good as that of the masterful Ray Harryhausen (though what stop motion work is?). The monsters are more crudely sculpted - especially around the head and face - and animated.
What's interesting to me is that, despite all these re-heated elements and the weaker effects work, I like this film quite a bit better than 7th Voyage. Sure Harryhausen's work in the earlier movie is superlative, but it's more-or-less the only real reason to see the film. Kerwin Matthews is kinda bland as Sinbad. He's much improved here and has better chemistry with his leading lady. This film's also quite a lot more light-hearted, often to the point of cheesiness, but in an unashamed, straight-forward way that I find quite endearing.
The basic premise is your usual "evil wizard tries to kidnap princess; heroic young man tries to stop him" stuff. If a family-friendly fantasy film is something you're looking for, then you should find a pleasant 90-minute diversion here.