Terminator Genisys is the fifth installment in a sci-fi action franchise that has blurred the line between sequel and reboot. At its start, this latest adventure feels most like a remake/reimagining. We open in 2029, with a human resistance movement led by battle-scarred John Connor (Jason Clarke) on the precipice of eliminating Skynet, the technology corporation responsible for billions of deaths and the bleak state of the world. Out of a number of volunteers, Connor picks Kyle Reese (Jai Courtney) to be the one to be sent back in time to 1984 to protect Connor's mother, Sarah (Emilia Clarke).

Running around Los Angeles in a pair of pants stolen from a hobo, Reese is not the only time traveler concerned with Sarah's well-being. As part of extended homage to James Cameron's original 1984 movie, we get a fairly ridiculous computer-animated version of Arnold Schwarzenegger's super muscular 1984 Terminator. That villain is soon dispensed by another Terminator, this much less CGI-embellished one bearing more resemblance to Schwarzenegger in his present state at age 67. This Terminator is known and loved as a father figure protector by Sarah, who is not the helpless waitress she was in a past 1984.

To save humanity, the brave Reese and Sarah will have to travel to the future. Reese convinces Sarah that they've got to beyond the judgment day of 1997 all the way to 2017, when Skynet is on the verge of launching Genisys, an operating system that will destroy mankind once and for all. With the "old, but not obsolete" good robotic Terminator, "Pops" to Sarah, passing the time to the old-fashioned way to regenerate some human flesh in his hand (and have his hair grow white), the trio reunites in post-apocalyptic 2017, where they reconnect with John Connor and discover the unexpected path that world salvation will take.

James Cameron declared Genisys the satisfying sequel his franchise has lacked since he turned over the writing and directing reins on 2003's Terminator 3: Rise of the Machines, but don't pay that endorsement too much mind, even if box office king of the world Cameron, who receives a characters credit and nothing more here, has little to gain from it (until 2019, when rights to the series return to him).

Genisys is penned by Laeta Kalogridis (Shutter Island, Alexander) and Patrick Lussier (a longtime editor whose few prior screenwriting credits include Dracula 2000 and its direct-to-video sequels). Each is new to the saga and largely unproven in the world of big budget, effects-driven spectacle, but together the pair shows obvious fondness and respect at least for the two Cameron-directed installments. Genisys harks back to the original film both in story and tone, recreating certain semi-iconic moments while also giving us a new perspective of the franchise-sparking events.

At no point can you agree with Cameron that this is the renaissance the world has waited nearly a quarter-century for. Still, Genisys is a passable piece of summer entertainment, buoyed by the return of the still charismatic and otherworldly Schwarzenegger and a reasonably engrossing plot you may or may not be fully able to follow. Though he does a better job for longer than you'd expect, director Alan Taylor (who transitioned from respected cable dramas to film on 2013's pretty good Thor: The Dark World) cannot overcome the fact that there's only so much a person needs to see of one indestructible character fighting another, each bouncing back from seemingly certain death on multiple occasions.

If the climactic action does not keep you enthralled -- and even in legitimate IMAX 3D, it lost my interest -- at least there have been some fun moments along the way, from classic Arnold one-liners to an update of Robert Patrick's once jaw-dropping T2 character to a small but inspired turn from recent Oscar winner J.K. Simmons as a veteran police detective whose on-point observations are treated like conspiracy theories by his younger higher-ups.

After seemingly putting the series to bed once and for all, Genisys cannot help but borrow a page from Marvel Studios' lucrative playbook and tease, mid-end credits, a sequel in the least coherent and committed way possible. Paramount Pictures, the fourth distributor to handle this series and one of today's biggest believers in tentpoles, already has untitled, uncast sequels scheduled for May 2017 and June 2018, although those plans seem impossibly optimistic and very much subject to cancellation.

Rated PG-13 like only its immediate predecessor, Genisys is nonetheless chockfull of violent action, albeit the kind with rapid regeneration rather than blood. Of the international cast, only Schwarzenegger gets to embrace his native accent and no one would have it any other way. Courtney's casting is a little strange since it recalls the sour note the universally-panned A Good Day to Die Hard left another treasured, productive '80s action franchise on. Ms. Clarke, reuniting with her frequent "Game of Thrones" director Taylor, cannot altogether hide her English accent or do much to convince us as a badass take-charge heroine. Still the four-personality family dynamic that drives the film is enough to get us to the finish line reasonably engaged and entertained.

Genisys may not be a smash hit or a critical darling (early reviews are even worse than they were on 2009's ill-received Terminator Salvation), but for a 31-year-old franchise of modest origin to still be spawning serviceable pieces of entertainment is no minor achievement.