The year is 2029, and John Connor, leader of the resistance continues the war against the machines. Directed by Alan Taylor and starring Emilia Clarke, Arnold Schwarzenegger, Jai Courtney and Jason Clarke. (Paramount Pictures)

Much like the “cybernetic organism” played by Arnold Schwarzenegger throughout the “Terminator” film franchise, a movie critic is only part living human tissue; the rest is ruthless killing machine. The human part, at least in theory, is capable of appreciating what everybody else goes to summer blockbusters for: action, jokes, cool special effects, suspense and emotion. The machine part must analyze plot, acting, character development, dialogue and other aspects of the film’s construction.

These dual roles are often at odds, with the robot side seeking out and blasting a film’s flaws with cold-blooded efficiency, and the mortal side sometimes wishing its other half would just put down the weapons and let the rest of us enjoy the ride.

In more ways than one, the battle between man and machine has never been so pitched as it is in “Terminator Genisys,” the fifth film in the sci-fi series that began in 1984 with a simple but gripping tale of a man trying to protect a woman from a time-travelling automaton assassin, sent from a post-apocalyptic future in which humans are at war with technology. The new film centers on a killer computer app called Genisys — imagine the “cloud” on steroids — but it’s also a schizoid mix of thrill ride and headache-inducing logic holes.

Part sequel, part reboot and part remake, “Genisys” is both seriously fun and seriously flawed. At the same time, it makes for a decent follow-up, at least to the first two films, which are generally considered to be the franchise’s best. (The less said about “Terminator 3: Rise of the Machines,” the better. The most recent sequel,“Terminator Salvation,” isn’t half bad.)

Emilia Clarke, of “Game of Thrones” fame, plays a fully formed, big-gun-firing Sarah Connor in “Terminator Genisys.” (Melinda Sue Gordon/Paramount Pictures)

“Genisys” begins, nicely enough, with a faithful recreation of the original film’s opening, following a prologue, set in 2029, that introduces us to some of the film’s new cast. Here, Jason Clarke plays John Connor, the leader of the human resistance against the robot army. Jai Courtney is Kyle Reese, Connor’s lieutenant, who is about to be sent back in time to protect Connor’s mother, Sarah (Emilia Clarke), from the cyborg hit man that has been sent to kill her, so that her son will never be born. Once again, the lethal robot is played by Schwarzenegger, whose younger, 1984 body — seen in all its naked glory — has been digitally spliced into the film.

This retro sequence is a giggle, even if it panders to easy nostalgia. But it gets better. Within minutes, Kyle discovers that the 1984 into which he has been dropped is not the familiar timeline of the first film. The scene is soon crowded with other, more advanced models of robotic “terminators” than Schwarzenegger’s prototypical T-101, including a version of the second film’s liquid-metal T-1000, played by Korean action star Byung-hun Lee. There are other surprises, and if you don’t want them spoiled, I’d avoid the entire Internet for the next few weeks, including all of the film’s over-sharing trailers.

In this alternate branch of time, Sarah Connor is no damsel in distress in need of saving, as she was in the first film. Here, the character is already the badass that actress Linda Hamilton morphed into in the second film. Unfortunately, Clarke — whose casting seems a cynical attempt to capture the actress’s young “Game of Thrones” demographic — isn’t quite as convincing as Hamilton’s “T2” heroine was. Even at 28, the British actress comes across as something of a petulant high-schooler, and she looks a little out of place wielding the big guns that the part requires her to handle.

More problematic is the whole time-travel element, which in “Genisys” takes on a much more prominent and, quite frankly, confusing role than in any of the previous installments. The new movie not only jumps from 2029 to 1984, but forward again to 2017, with detours — courtesy of miscellaneous memories, flashbacks and dialogue allusions — to 1979, 1997 and 2014.

It’s hard to keep track of all the threads at times, even, apparently for some of the film’s characters. “How can I remember a past I’ve never lived,” asks Kyle, who after showing up in 1984 starts hallucinating a childhood far more halcyon than the one he used to think he had. “I’ve got to know what’s going on,” bemoans a cop (a wonderfully befuddled J.K. Simmons), who, in 2017, suddenly remembers meeting Kyle and company way back in 1984. “We’re here to stop the end of the world,” Sarah replies, essentially telling him to let it go. I suggest you do the same.

Time travel is always a risky proposition. It’s easy for filmmakers to get carried away, and to hope that the audience won’t notice the necessary cheats. In “Genisys,” it feels a bit like director Alan Taylor (“Thor: The Dark World”) just doesn’t care about the little loopholes he leaves in the film’s pell-mell rush from one calendar entry to another. The script, by Laeta Kalogridis (“Shutter Island”) and Patrick Lussier (“Drive Angry”) is so far from airtight, there’s practically a breeze.

But there are also many pleasures, the deepest of which come courtesy of Schwarzenegger’s enduringly fun bionic warrior which, like a classic wooden roller coaster, gives a reliably rousing, if at this point somewhat rickety, ride.

James Cameron, who co-wrote and directed the first two films before disappearing, was wisely brought in as a kind of character consultant by Skydance Productions. The touch of the “Terminator” creator is apparent here. “Genisys” goes back to what made the franchise work in the first place: not the machine inside the man, but vice versa.

PG-13. At area theaters. Contains violence, partial nudity and brief crude language. 125 minutes.