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Presumably it was the incredible popularity of gaming nowadays that led Disney to believe that a sequel to 1982’s “Tron,” the first prestige picture about video games, would be a good idea. Certainly nobody was clamoring for one; the original picture, despite lots of then-“state-of-the art” effects (which look pretty feeble now), was a disappointment to both studio, which was looking for a blockbuster, and audiences, who found it a high-tech bore. As it turns out, despite nearly three decades of visual improvements and the added attraction of 3D, “Tron: The Legacy” doesn’t look all that great, and in narrative terms it’s a tired retread out of the “Star Wars” handbook.

The youthful hero of the piece is Sam Flynn (Garrett Hedlund), who has daddy issues because pa Kevin (Jeff Bridges), the computer whiz, abruptly disappeared one night years before. (We know, of course, that Kevin was sucked into that great video game with light-cycles, Frisbee combat and the great warrior Tron.) In reaction Sam’s become a rebel who regularly embarrasses his father’s old company, which has gone the bottom-line route rather than remaining innovative and socially-conscious, with some mischievous hacking. (He also has the physique of an Olympian and top motorcycling skills.)

One day Sam’s contacted by his dad’s old pal Alan Bradley (Bruce Boxleitner), who directs the kid to his father’s old arcade, where he discovers the old man’s computer console and is promptly sucked into the Tron-world, too. Taken for a runaway program, he’s forced to compete in the dangerous games until he’s recognized by the ruler of the computer world, Clu, a program clone created in the image of the young Kevin that rebelled against its maker and has taken control of the realm in order to perfect it—his original purpose as designed by Kevin, but one he’s now interpreting in a destructive fashion that included liquidating an entire race of beings that simply appeared on the scene.

Clu, as is explained, forced Kevin into hiding and has ever since been trying to locate him to secure his personal disc that can be used to transport Clu and his army of programs to earth, which he intends to perfect. If I understand things aright, it was he who lured Sam into the computer world to use him as bait while opening the portal to earth, and when Sam is rescued by Quorra (Olivia Wilde), the only surviving member of the beings Clu had tried to wipe out and now the aging Kevin’s sole disciple, and taken to Kevin’s secret abode, the trap is sprung.

From this point “Tron: Legacy” turns into a chase movie, with Kevin, Quorra and Sam trying to escape to earth through the portal before it closes again and thereby prevent Clu from launching his attack. Their effort involves an attempted agreement with Zuse (Michael Sheen), the flamboyant proprietor of the computer world’s with-it sky-bar for transportation, and pursuit of the good guys by Tron (Boxleitner’s masked stand-in), who’s been brainwashed—or reprogrammed—into serving as Clu’s chief enforcer. The eventual outcome is a final lap in which a computer airship carrying our heroes is pursued by Clu’s fighter planes while Sam uses his gamer experience to shoot them down. It’s very much like the sequence in which the rebels attack the Death Star in the first “Star Wars” movie, but much less exciting.

There are other echoes of Lucas’ movie, too, especially in the father-son dynamic. Sam’s a frustrated young man, much like Luke Skywalker, and Hedlund is as blandly anonymous playing him as Mark Hamill was. As for Bridges, he gets to do both the Obi-wan Kenobi part, as the aging Kevin, and the Darth Vader role, as the malevolent Clu. But he’s not particularly good at either. Old Kevin gets off a few amusing lines, but not many, and in serious mode he’s rather tedious. Bridges plays Clu via motion-capture software that superimposes his computer-generated younger face on a thinner body, and the result is a plastic simulacrum—perhaps appropriate in the case of a clone, but not so much in the shots (such as the prologue, set in 1982) when the same artificial visage is given to the supposedly “real” Kevin. In her skin-tight outfit Wilde is attractive eye candy in the Milla Jovovich mode, but nothing more. And what to make of Michael Sheen? This talented English actor camps it up in a way that suggests he’s trying to do a one-man Cantina show; together with his turns in the “Underworld” movies, this performance suggests he doesn’t have many standards—or inhibitions. It’s embarrassing.

Of course, the human beings are secondary in this movie. It’s the effects that matter, and frankly they’re not all that great. The humanoid programs explode into little atoms when defeated, which doesn’t much impress, and the aircraft at the end look rather like Wonder Woman’s invisible plane, all outline and no body. The whole computer world has a dully metallic look, and Clu’s big rallies resemble nothing more than Nuremberg pageants. Overall, the images have size but no grandeur. The 3D doesn’t add much to them, either. (Incidentally, some parts of the picture—those set on earth at the beginning and end—are shot in 2D. Though you’re instructed to wear your 3D glasses during them, you’d be well advised not to. They look much brighter and crisper without the scrim the lenses cloud them with.)

There’s plenty of unintelligible talk about ultra-complicated algorithms in “Legacy.” But all you have to know about it is a simple equation: “Tron x 2= Bomb Squared.”