In the Terminator saga, the world has been taken over by intelligent machines bent on eradicating humans; with the 25-year-old Terminator franchise, the machine culture has won and the actors are just replaceable parts. Christian Bale takes over for Nick Stahl (who took over for Edward Furlong) as John Connor, the rebel leader mythologized as humanity’s only hope (except for those other two dudes, I guess). As directed by McG (Charlie’s Angels), this fourth installment begins with lots of hardware and firepower and lets up only long enough to put across a tired time-travel plot in which Connor must rescue a teen who’ll journey back to 1984 and father him. The movie’s only unmitigated pleasure is a too-brief fight scene between Connor and a naked combatant made up to look precisely like Arnold Schwarzenegger, the relentless cyborg of the first three installments. With Sam Worthington and not enough of Common, Jane Alexander, or Helena Bonham Carter. PG-13, 115 min.