The by-the-numbers plot features a villainous Premier who wants to take over the kingdom from the Princess' dying father, the King, but has to first contrive a way to marry the Princess. To do that, he has to use his cohort, the Black Pirate, to waylay the ship of the Princess' intended bridegroom, the Prince of Thailand. "Sinbad" intervenes every step of the way, with the help of Sennin, the old wizard, who is especially useful in battling the magic of the old witch, Granny, who's working for the Premier. (Sennin can turn into a fly at will, while Granny can turn people to stone.) Sinbad's motive is the retrieval of a chest of jewels stolen from him by the Black Pirate and passed on to the Premier who has given some of the jewelry as a gift to the Princess. The action culminates in a bit of derring-do in which Sinbad attaches himself to a sturdy kite and flies over the castle walls to initiate an attack by the rebels on the night of the Premier's intended wedding to the Princess.
The plot moves at a moderately steady pace, but there is little urgency or suspense. Sinbad is somewhat aloof and never seems to feel he's in much danger, even when he's imprisoned and made to do slave labor. Other than the chest of jewels, he doesn't seem to have much of a stake in the action. There are three different beautiful women who are his allies at one point or another in the film, yet he never bothers to romance any of them.
Up until the final battle, there is simply not enough action. There are some fights and confrontations, but they're not terribly well-staged and they happen very quickly. Toshiro Mifune gets to wield a sword with great vigor in the final battle and performs some judo maneuvers much earlier, but, overall, he seems somewhat restrained here.
The lavish interior sets and the elaborate miniatures of the castle exteriors and the magnificent ships are all very impressively created. The special effects are best in the scenes involving the magic employed by the wizard and witch, particularly in the transformation scenes, but suffer whenever process work (rear screen projection) is required, such as the shots of Sinbad strapped to the kite and bearing down on the castle. Overall, for a fantasy film it just doesn't have the exuberance and sweeping imagination of American-made fantasy films of the same era, such as JACK THE GIANT KILLER (1962), CAPTAIN SINDBAD (1963) or even the ultra-low-budget THE MAGIC SWORD (1962).
The real treat here for fans of Japanese cinema is the all-star cast. Toshiro Mifune heads the list, of course, but he is joined by such other stalwart Japanese character actors as Makoto Sato (MESSAGE FROM SPACE), as the Black Pirate; Satoshi Nakamura (THE MANSTER) as the head of the archers; Jun Tazaki (KING OF THE MONGOLS) as a spirited guardsman who is alternately an ally and opponent of Sinbad; Tadao Nakamaru as the Premier; and perennial villain Eisei Amamoto ("Dr. Who" in KING KONG ESCAPES) as the witch. Of this group of actors, Ichiro Arishima comes off best as the horny old wizard, Sennin, a character who is clearly the model for--or derived from the same source as--Master Roshi of animated "Dragon Ball Z" fame.
Best of all are three beautiful actresses who are fan favorites from the era: Kumi Mizuno (MONSTER ZERO, FRANKENSTEIN CONQUERS THE WORLD) as the rebel leader; Mie Hama as the Princess (and looking very lovely in a dazzling array of costumes); and Akiko Wakabayashi as the Princess' loyal maid. Hama and Wakabayashi occasionally appeared in Japanese films together (KING KONG VS. GODZILLA) and are best known to western audiences for co-starring with Sean Connery in the fifth James Bond movie, YOU ONLY LIVE TWICE (1967).
I should point out that the English dubbing on LOST WORLD OF SINBAD is below average. Paul Frees does Toshiro Mifune's voice as if he's got a noose tightened around his neck and the others aren't much better. The attempts to do "Japanese" accents are particularly grating.
I watched this on a Japanese-only DVD (no subs.), with a bootleg VHS of the English dub providing the soundtrack. I'd much prefer a subtitled DVD.