I must confess that the attraction of this oddball quartet of superheroes—the full title of “Teenage Mutant Ninja Turtles” tells it all—has always eluded me. But whatever the cause, the “TMNT” became a goofy pop phenomenon in the 1980s, starting out in comics and then morphing into an animated TV show. And in the early nineties several live-action movies were made, with guys in rubber suits taking over for the drawn characters. The chintzy, clunky trio of flicks deservedly sent the team into the cinematic afterlife.

But superheroes, even ones with shells, have a habit of rising again, and so the turtles are back—this time in full CGI-animation form. Visually the result is an improvement on the rubber suits, but in all other respects “TMNT” is no better than its predecessors.

The story begins with a prologue explaining the threats our heroes will face, an exposition is so laboriously complicated that a pop quiz after it’s over would probably stump everyone but the most devoted fan. Suffice it to say that the well-being of the world depends on confronting an immortal king-turned-industrialist named Winters (Patrick Stewart), who’s revivified four sleeping stone giants, once his generals, to capture thirteen monsters that, when hurled into some sort of dimensional portal, will loose grave evil on earth. (How these critters have apparently gone unnoticed for millennia is never explained, as far as I can tell.)

The turtles, unhappily, are divided at the moment, with Leonardo (James Arnold Taylor) in the Amazon jungle learning leadership skills at the insistence of their wise master, the elderly sewer rat Splinter (Mako). In his absence his brothers have taken different routes, with goofy Michelangelo (Mikey Kelley) becoming a children’s party performer, lazy Donatello (Mitchell Whitfield) getting a job as a computer tech adviser, and only surly Raphael (Nolan North) continuing the family superhero business in the guise of a heavily-armored vigilante called Nightwatcher. He’s sometimes helped in this pursuit by the lovably dim-witted human Casey (Chris Evans), the boyfriend of svelte April O’Neal (Sarah Michelle Gellar), an archaeological expert who’s been collecting Winter’s four statues for him. The plot proper starts when Leonardo returns to the Big Apple, but as Splinter informs him, the quartet has to train to work as a team again before going back into action—something that Raphael, angry over Leonardo’s long absence and unwilling to take second fiddle to him again, obstinately resists. So before the guys—along Splinter and April—can take the field against Winter and his minions (who include a bunch of ninjas), Leonardo and Raphael have to work out their fraternal differences.

This complicated but tedious plot lacks both imagination and excitement. And spending so much time on the hostility between Leo and Raph is frankly ludicrous; these are turtles, after all, and the effort to delve into their psyches comes across as totally absurd. To make matters worse, the surfer-dude dialogue the brothers toss around, which might have seemed kind of cool twenty years ago, now comes across as lame. And the comic relief that Casey is supposed to provide isn’t very comic, nor does it provide any relief. The character animation is decent enough, with the turtles and Splinter impressing far more than the “human” characters, but the backgrounds are rather disappointing, especially since most are so dark and gloomy that they give the entire picture a drab, dismal feel. The voice work is at best adequate, with Stewart and Gellar, despite their high-recognition names, scoring rather low. And it’s sad that this will be one of the last appearances of so distinguished a veteran as Mako on the screen.

Marine biologists tell us that some turtles live for a very long time, but on the evidence of this bewilderingly complicated but curiously pedestrian movie, the teenage mutant ninja variety has definitely passed its prime.