Replaces Living Legend with original Mysteries of the Zone main storyline from Call of Chernobyl. In case you are not in the mood to see the undying Strelok again.
Everything else is all about same oldschool hardcore pick up intel, lie down, rest and watch Sidorovich tiktok dance video, get up and move on to the next checkpoint.
For those who are not familiar with original CoC playthrough - Strelok is dead, you receive what is left of his possessions from Doctor and from that moment operate completely on your own. I don't find this plot very interesting (still 90% freeplay which is fine by me), but it is a bare minimum motivation to push to the north. One life Ironman game mode helps digest oversimplified story.
Quest order is not strict. It is possible to collect documents from labs and disable brainscorchers before talking to Doctor.
What is more important - this story mode works with warfare (except some Monolith wishes) so you are free to capture Zone first, before starting adventure.
Collected documents are not for sale, they are required to enter warlab.
Better to use JSGME so it can be easily reverted back to LTTZ at any time.