The Day the Earth Stood Still II – sequel to the original Robert Wise film, not the awful remake. Klaatu returns from the stars years later and offers the human race a selection of robot policemen, with the warning that they’ve done modelling on our civilization, and don’t see it lasting out the century without their help.
Forbidden Planet II – Altair IV may be gone, but there’s enough new technology to be gained from retro-engineering Robby that it transforms life in Human Space.
Metropolis II – Joh Fredersen has been somewhat reformed by his experience, his son Freder is now a Mediator, and presumably Unions have gained new power. But the Heart machine is broken, the Worker’s City is flooded, and Metropolis has to be rebuilt. Rotwang is dead, but they have his technology and his notes. Now what the hell happens? The original film left an awful mess.