20,000 leagues under the sea

If you thought the animated undersea critters in "The Life Aquatic With Steve Zissou" looked too fantastic for belief, here's a news flash: They're on the conservative side compared with the actual life forms in "Aliens of the Deep," the new IMAX 3-D documentary by James Cameron and Steven Quale.

Mr. Cameron has been fascinated by oceans for ages, going back at least as far as "The Abyss," his 1989 epic. Never embarrassed to revisit an old interest - or recycle an old title - he directed the 3-D spectacle "Ghosts of the Abyss," about a real-life probe of the Titanic wreck, two years ago.

Cameron does better in "Aliens of the Deep," another visual extravaganza that would jolt your retinas even if it didn't have the towering IMAX screen and vivid 3-D process at its disposal.

Tucked into compact "submersibles" with highly educated companions - marine biologist, oceanographer, and the like - Cameron travels to parts of the ocean no scuba diver could ever plumb. Their lights shine on all manner of beings that few human eyes, if any, have beheld before. Some are as gorgeous as can be. Others are so ugly that you're glad the sun's light never shines this far below the surface.

Even though Cameron soft-pedals the bogus "drama" that watered down "Ghosts of the Abyss," he dilutes the new movie's impact with material that's really not needed, including a hymn to the sun at the beginning and a lot of animated space-exploration material - looking like outtakes from "AI: Artificial Intelligence," the Steven Spielberg fantasy - at the end. I also found Jeehun Hwang's music score distracting as it switched between imitation Philip Glass minimalism and imitation György Ligeti modernism a la "2001: A Space Odyssey."

These shortcomings aside, "Aliens of the Deep" is a major treat for the eyes. Also worth noting is the ongoing success of Imax 3-D in the limited number of theaters equipped to handle it. Neither the super-huge screen (Cinerama) nor 3-D technology (with red- and blue-lensed glasses) found many partisans when Hollywood floated their early incarnations in the 1950s, but they've taken hold in a different way today. The latest example is a worthy one.

• Rated G.