Terminator Genisys aTime travel — ugh.

Terminator Genisys, the latest installment of the humans vs. robots saga, riffs heavily on elements from the first two James Cameron-helmed movies in the series and largely (and wisely) ignores the third and fourth movies. It opens with humanity’s defeat of Skynet in the post-apocalyptic future, the discovery of the malevolent A.I.’s last-ditch attempt to rewrite history, and mankind’s savior John Connor (Joseph Clarke) sending his second-in-command and father-to-be Kyle Reese (Jai Courtney) back in time to save his mother, Sarah Connor (Emilia Clarke) from a cyborg hitman, procreate with her, and ensure the course of future events.

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That familiar set-up takes a left turn when an unexpected event lands Kyle in an alternate timeline in which multiple Terminators have been sent throughout Sarah’s timeline, including an old-school T-800 model (Arnold Schwarzenegger) reprogrammed by an unknown source and sent to protect her.

Reese seems largely redundant at this point, and his mission is skewed by the altered history. Somehow Skynet has set itself up to rise in 2017, rather than 1997, and it has a new weapon at its disposal: John Connor himself, compromised and converted into a next-generation Terminator.

Ideally there should have been a “SPOILER” alert before that last part, but that little detail was inexplicably ruined in a trailer for Genisys, robbing the movie of what might have been its most compelling plot twist. The movie never quite recovers from the loss of what should have been a “WTF” moment, and is further hamstrung by the screenwriters’ unwillingness to fully explore the possibilities they so tantalizingly open up.

The notion of alternate timelines and whether or not set events can truly be altered is a tantalizing one, and exactly what the franchise needs for a successful reboot. Instead, it recycles past events and familiar dialogue, glosses over the anxiety-inducing bigger picture of transhumanism, leaves too many questions unanswered, and uses so-so action sequences to draw our attention away from gaping plot holes and lapses in logic. (Why time travel to 2017 and battle Skynet head on when you could arrive in, oh, say 2010 and take your time bringing it down before it’s born. Yeesh — no wonder the machines are winning in the future.)

Arnie is largely a supporting player this time around. It’s the two Clarkes who carry the movie, and both give their all against the lackluster material. It hardly matters though, as the two characters have been interpreted and re-interpreted so many times — and played by several different actors over five films and a TV series — that there is no consistency to them, and thus little to for the audience to connect with. Emilia fares the best, channeling her inner khaleesi to nail Linda Hamilton’s grit and determination. Courtney still has that generic action hero feel about him, and often fades into the background. J.K. Simmons and Matt Smith are given some interesting roles that get too little screen time.

Terminator Genisys is the first of a planned trilogy; as such, it makes the same mistake as Amazing Spider-Man 2 and other over-confident blockbusters: It assumes that a sequel is a foregone conclusion and punting its loose ends downfield to be sorted out later.

All things considered, that seems a bit optimistic.