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The good news is that this third installment of the “Twilight” franchise based on Stephanie Meyer’s popular novels is the best yet. The bad is that’s not saying much.

What’s improved in “Eclipse” is mostly the technical side. With an obviously bigger budget to hand, the SFX, coordinated by Alex Burdett, and visual effects, supervised by Crystal Dowd, are on a larger canvas and are more effectively and seamlessly deployed. (It’s no surprise that no fewer than eleven effects outfits are credited.) And director David Slade, working with cinematographer Javier Aguirresarobe, gives the picture a degree of grandeur in the widescreen images that was largely lacking in the earlier movies.

But nothing else here shows much of an advance. The plot is absurdly thin, consisting of two interrelated elements. One is the continuing romantic triangle involving angst-ridden vampire Edward Cullen (Robert Pattinson), his human squeeze Bella Swan (Kristen Stewart), and her native American admirer (and werewolf-boy) Jacob Black (Taylor Lautner). The two guys are, of course, always at each other’s throat, in a manner of speaking, with Bella drawn to both and trying to keep them from killing one another.

The only other narrative strand is the targeting of Bella by vengeful red-haired vampire Victoria (Bryce Dallas Howard, replacing Rachelle Lefevre), who’s still peeved over her role in the demise of her lover James in the first picture. To achieve her aim, Victoria creates a small army of bloodsuckers from young victims in Seattle, beginning with clean-cut Riley (Xavier Samuel), whom she makes her lieutenant, using him to create a band of powerful “newborns” whom she’ll employ to destroy the whole Cullen clan. To protect Bella from her, Edward and Cullen strike a truce between those inveterate enemies, vampires and werewolves (or, I suppose, more accurately shape-shifters). The result is a big climactic battle fought tooth and nail, as it were, though Bella and Edward must face off against Riley and Victoria pretty much alone. And observing the confrontation are four representatives of the Volturi, that vampire coven that oversees undead activities as umpires—though not, it appears, very dependable ones; they’re led by Jane (Dakota Fanning), a tight-lipped lass who will presumably have more to do in later installments than merely glower and spit out orders, as she does here.

This is extremely silly stuff, and one devoutly wishes it were played even slightly tongue-in-cheek, employing the light touch with whom Joss Whedon leavened his TV shows “Buffy” and “Angel.” Alas, the only shafts of humor here are pretty sophomoric, barbs tossed between Edward and Jacob and the befuddled observations of Bella’s concerned dad Charlie (Billie Burke), who prefers he-man Jacob to swooning romantic Edward. (You might be moved to giggle at certain points, but it will be because of the ridiculousness, not because laughter is intended—watch especially for the two horrendous “He/she deserves to know” moments.) And the grim earnestness with which the movie’s generally played is a particular problem when the dialogue is so awful. Not having read the books, I don’t know whether Melissa Rosenberg lifted it from the tomes, but if so, she should quickly have sent it back, and if not, she should be ashamed to have written such an avalanche of cliches and howlers.

And it’s recited with the goofy intensity characteristic of daytime soap opera. Pattinson again goes the suffering, soulful James Dean route, though he does manage to occasionally crack a smile here, and gets off one good joke about Jacob’s predilection for going about shirtless—which is probably the thing most female viewers will best remember about Lautner’s performance, though he smolders well enough. Stewart is, once again, tediously gloomy; yes, Bella’s kind of a drag, but she needn’t be as dreary as this. Of the supporting cast, Burke gets a few easy laughs; most of the others are nondescript, with the exception of Samuel, who gives Riley a touch of real emotion, and Jackson Rathbone, who as Jasper, the long-haired strategist of the Cullen clan, uses an extended back-story flashback to make his character more interesting. Even Howard and Fanning, more experienced than most of the young cast, offer nothing of interest—though in their defense it must be admitted that the script gives them few opportunities. All of which suggests that Slade either isn’t as skilled in eliciting strong work from actors as 2006’s “Hard Candy” indicated, or he too was simply defeated by the material.

The first “Twilight” movie was basically “Wuthering Heights” and the second “Romeo and Juliet.” This one isn’t much more than “Dracula Vs. the Wolf Man” mixed up with a John Hughes high-school romance. But at least it looks better than the previous two.