“I’m old, not obsolete,” mutters Arnold Schwarzenegger’s aging android in “Terminator Genisys,” and his words could be a wishful mantra for this nervy, silly, almost admirably misguided attempt to give the 31-year-old franchise a massive cybernetic facelift. More or less rewriting everything we thought we knew about the Connor genealogy, the properties of liquid metal, and the rules of post-1984 time travel, this f/x-encrusted reboot feels at once back-to-basics and confoundingly revisionist, teeming with alternate timelines and rejiggered character histories (the most perplexing of which finds Sarah Connor now continually referring to Schwarzenegger’s Terminator as “Pops”). Consider it the 3D blockbuster equivalent of disruptive technology, and while online fans have already voiced their displeasure, the movie’s willingness to veer crazily off-course feels less objectionable than the monotony and sense of self-parody that kick in long before the whimper of a finish.

The return of a top-billed Schwarzenegger (here playing three different versions of his most iconic role) should lend Paramount’s July 1 release a bit more box office oomph than Warner Bros. managed with “Terminator Salvation” (2009), which the actor skipped while finishing the second term of his political career. Still, a mere six years after that poorly received mediocrity (the movie, not the political career), it’s safe to say the “Terminator” movies weren’t exactly crying out for this sort of extreme overhaul. And in a season when the studios have been busy updating their pre-millennial action-cinema touchstones, it’s unlikely that this new film will find itself in the same commercial league as “Jurassic World” and “Mad Max: Fury Road,” let alone the next chapter of “Star Wars.” That Paramount has positioned “Genisys” as the start of a new “Terminator” trilogy can’t help but smack of undue optimism.

Fan uproar aside, the series’ underlying mythology is hardly an inviolable one, and for a while it’s easy to admire the daring with which screenwriters Laeta Kalogridis and Patrick Lussier shake things up and reframe the events of the earlier films from a bizarre new perspective. Exploiting the narrative possibilities of time travel on a more vigorous and elaborate scale than its relatively self-enclosed predecessors, “Genisys” effectively returns us to the events of James Cameron’s “The Terminator” (1984), stirs in the buddy-Arnold dynamics of “Terminator 2: Judgment Day” (1991), borrows the man-machine-hybrid plot device from McG’s “Terminator Salvation,” and more or less pretends that Jonathan Mostow’s “Terminator 3: Rise of the Machines” (2004) never happened (“never happened” being an admittedly unstable concept in this particular universe).

Accompanied by a familiar blast of Brad Fiedel’s original “Terminator” theme, a prologue solemnly announces that 3 billion people died in the nuclear conflagration of Judgment Day on Oct. 29, 1997. Some 30 years later, the malevolent machines of Skynet are losing the war with a surviving remnant of humanity, led by an impassioned revolutionary named John Connor (Jason Clarke, his face marked with scars). So far, so familiar — except that when Kyle Reese (Australian actor Jai Courtney) gets zapped back in time to rescue John’s mother, Sarah, a last-minute twist suddenly alters his trajectory: When Kyle lands in a dark Los Angeles alley in May 1984, the machines are already waiting for him in the form of a lethal T-1000 who possesses blades for hands, reconstitutes himself at will, and is played by Korean star Byung-hun Lee. (Clearly, this version of Skynet isn’t just self-aware, but also hip to the realities of the all-important Asian movie market.)

Working with a crew that includes production designer Neil Spisak and cinematographer Kramer Morgenthau, director Alan Taylor fastidiously re-creates individual shots and scenes from Cameron’s 1984 movie — right down to the appearance of the evil T-800, achieved with a massive silicone replica of a nude, bulked-up, 37-year-old Schwarzenegger. But before the T-800 can do any real damage, he’s ambushed by Schwarzenegger’s slightly older, leaner good-guy Terminator, treating us to the brief spectacle of an Arnold-vs.-Arnold faceoff before Sarah Connor (English actress Emilia Clarke, “Game of Thrones”) steps in to finish the job. Turns out Sarah has been under the protection of her Austrian-accented guardian since she was 9 years old, and she knows full well that Kyle has come back in time to save her life and inadvertently father her child. She even gets to bring some gender parity to the proceedings by uttering the signature line “Come with me if you want to live!”

All this unfolds in an unusually cheeky, self-conscious register, and “Terminator Genisys” proves most diverting (or, depending on the viewer, infuriating) when the characters are trying to make sense of who they are, what they’re doing and what will or won’t happen as a result — none of which will mean much to a viewer coming in with no prior knowledge of the series. The movie does give us an enjoyably dumb crash course in time-travel specifics that explains how a “nexus point” can give rise to parallel timelines and alternate memories, opening a narrative wormhole that’s intended to justify the movie’s wholesale reimagination of its material. (It’s roughly the same gambit J.J. Abrams pulled off, albeit much more cleverly, in his 2009 “Star Trek” relaunch.)

In the refurbished “Genisys” timeline, Judgment Day has been postponed from 1997 to 2017, the same year that Skynet plans to seize control via a spiffy new worldwide operating system called Genisys — a twist that neatly updates the series’ techno-paranoia for the smartphone era. And so Kyle and Sarah make their way to San Francisco circa 2017, where Pops is now played by a conspicuously older and grayer-looking Schwarzenegger (as the film helpfully notes, the hardware is willing but the flesh is weak). Amid this web of Silicon Valley intrigue, they also run straight into John Connor himself, who welcomes Mom and Dad with open arms — and not in an altogether reassuring way.

To summarize the plot further would risk inflaming the reader’s outrage and probably give all of us a massive headache. Suffice to say that, in arranging this vaguely Oedipal family reunion, “Terminator Genisys” aims to reset the entire franchise by eliminating John Connor’s revolutionary heroism as the narrative constant around which everything else must revolve. In eliminating this premise, however, the filmmakers don’t offer much in the way of compensation: The what-the-hell invention of the first half gives way to a growing sense of desperation in the second, as our heroes find themselves running from one skirmish to the next, while the baddies keep showing up and finding new ways to say “You can’t win!” before going up in flames. For his part, Taylor orchestrates the action sequences with the same stolid proficiency he brought to “Thor: The Dark World,” whether he’s staging a massive vehicular smash-up on the Golden Gate Bridge, or filming the gleaming puddles of CGI that ooze from the Terminators’ rapidly mutating bodies.

For all its initial playfulness, the script never rises to the level of surreal, cortex-tickling pleasure it seems to be aiming for, and for all its self-awareness it’s weirdly devoid of humor. Even the possibilities of naked coed time travel — and the potentially world-altering consequences of whether or not Sarah and Kyle hook up — seem to evince more embarrassment here than amusement or pleasure. (The nudity, like the violence, is strictly PG-13.) What comedy there is unfortunately comes mostly from Schwarzenegger, straining as ever to turn his utter humorlessness into a source of humor, and at one point trying to add “Bite me” to the immortal “Terminator” lexicon. Still, the star does what he’s here to do — namely, imitate a lethal slab of granite and ensure a measure of continuity with the rest of the series — even as he largely cedes the spotlight to Courtney’s hunky earnestness, Jason Clarke’s unsettling intensity, and Emilia Clarke’s semi-successful attempt to channel the fire and grit of Linda Hamilton.

It is, on the face of it, a ludicrous and faintly depressing spectacle, like watching a “Terminator” highlights reel stiffly enacted by Hollywood’s latest bright young things (which makes the appearance of J.K. Simmons all the more welcome in the minor role of a police detective). Yet while “Terminator Genesis” is far from a perfect movie, it may well be a perfect product of its time and place, one that ably reflects the ruthless economy of the industry in general and the thematic logic of this series in particular. The “Terminator” franchise, by now, has become its own worst Skynet — a monument to self-regeneration that endlessly repackages the same old thrills in ever sleeker, sexier models, and that gladly screws with its own past to ensure its future survival. You can’t quite call it obsolete, perhaps, but damned if it doesn’t feel awfully futile.