Spoiler warning for the events of the first twoI Know What You Did Last Summermovies.
Nostalgia Sells, But Is It Enough?
Its easy to see why Hollywood execs would sign off on these projects.

Columbia Pictures
Basically, nostalgia sells and its an easy way to make a quick buck.
Objectively speaking, that would depend on whether or not the story can be expanded upon.
They are eventually hunted one by one by a figure in a fishermans slicker wielding a hook.

Julie and Ray manage to survive when the killer is thrown off his fishing boat into the ocean.
Helen and Barry were killed just as the films final act began.
Fortunately, Ray shows up just in time to save the day.

Columbia Pictures
When Ben tries to stab him, he accidentally kills his own son.
The distraction gives Julie time to pick up a gun and shoot him.
That ending could be interpreted in many ways.
If one wanted to end the story, it could be written off as a dream.
It could also be another member of the Willis family out for revenge.
Since Hewitt and Prince are returning for the legacy sequel, it will probably be the latter.
Learn more about the I Know What You Did Last Summer sequel here.