Grade: B-

It’s back to the future with Disney’s animated offering for the summer of 2001, a fairly straightforward action-adventure comedy (minus songs and talking animals) about a group of intrepid explorers who make their way to the underwater realm of Atlantis and find romance, danger and excitement there. Set in the period immediately before World War I, the story, penned by Tab Murphy (who previously wrote the “Tarzan” screenplay) has the feel of one of Jules Verne’s fantasies–not unlike “20,000 Leagues Under the Sea,” which Disney filmed so memorably in live-action form in 1954. This time around, however, the third act of the piece has been given a distinctly New Age twist, which–to be honest–doesn’t come off awfully well. And, of course, the picture has been made using the most advanced digital animation techniques. You could say, therefore, that “Atlantis: The Lost Empire” is a pretty old-fashioned piece that’s been given a contemporary twist in terms of both the storytelling and the filmmaking. The result, like last year’s “Titan A.E.,” looks great, but comes up a bit short in narrative terms (though not quite as short as Don Bluth’s picture did).

The hero is one of Disney’s lovable bumblers, Milo Thatch (voiced by Michael J. Fox), a museum maintenance man who wants to continue his late grandfather’s search for the legendary lost civilization that Plato talked about. Eventually he’s bankrolled by eccentric millionaire Preston Whitmore (John Mahoney) and teamed up with a crew of well-armed mercenaries led by Commander Rourke (James Garner) to locate the submerged city. Despite the perils of the journey, the expedition succeeds, and Milo soon finds himself romantically involved with Princess Kida (Cree Summer), who’s slated to succeed her elderly father (Leonard Nimoy) as ruler of Atlantis. There’s a sudden twist, however, as the city is threatened by interlopers trying to steal the realm’s mystical energy source, dooming the population. Can Milo and Kida save the day and live happily ever after? Hey, guys, things may have changed a lot in the Mouse House in recent years, but this is still a Disney film.

What’s most impressive about “Atlantis” are the visuals. The picture represents a seamless merging of conventional, hand-drawn animation and computer-generated images, and especially in the widescreen format, the result is truly impressive. Several sequences stand out, among them a tour-de-force in which the expedition’s huge ship is attacked by what seems to be a giant lobster; and the culminating confrontation between good and evil, despite its narrative flaws, is also eye-catching. Unhappily, the story and characters don’t match the picture’s alluring appearance. The first half is the better of the two: it has a good mix of humor and heart, Milo is endearingly awkward, and a few of the secondary members of the expedition–especially the wonderfully deadpan Don Novello as oddball explosives expert Vinny Santorini–are given some fine, funny lines. But once the group makes its way to Atlantis, things go sour in more ways than one (I hesitate to spoil readers’ enjoyment by revealing too much about plot twists, so I won’t be specific about changes in individual characters except to say they’re not always convincing). The underwater city itself is not a terribly interesting environment, and all the rigmarole about the mysterious power source, which involves some rotating globes and monoliths that might be refugees from Kubrick’s “2001,” has the feel of something you might run into on the Psychic Friends network. To make matters worse, Milo begins to grow wearyingly inept, Kida doesn’t prove much of a character, and the denouement escalates into a full-blown battle chock full of the sort of explosions, gunfights, high-speed chases and fisticuffs that might be better suited to “Charlie’s Angels” or “The Matrix 2.” (Parents should be aware that the picture is rightly rated PG, and, with what seems to be a fairly high body count, isn’t appropriate for toddlers.) The upshot is that despite all the visual excitement and high-flying (or floating) action set-pieces, the last part of “Atlantis” grows increasingly chaotic and empty. Even a heavy-handed message about valuing culture and environment over destructive greed can’t overcome the messiness.

Still, “Atlantis” is worth seeing for the splendid animation and some vivid characterizations, whatever its narrative weaknesses. (If the picture does nothing else, it should revive Novello’s career; I sure wouldn’t mind seeing Vinny in some sort of spin-off.) Unlike its namesake, it doesn’t sink like the proverbial stone, but–especially in the second half–it has some trouble staying afloat.