Instead, they've add a whole new set of characters, (what seems to be) a new plot line, and another set of confusing "flashbacks" or "alternate reality" scenes.
That's called the Season Premier. Every season has started at, or back at, the beginning, introducing a new cast and storyline.
This time we seem to have two new casts. The cast in the temple and the pod people/dopplegangers that have replaced the passengers on flight 815. While the differences in Charlie, Jack, Shannon and Boone are small, the new Hugo-"Never have any bad luck"-Reyes is not the Hugo we've been following the last 5 seasons.