At its further reaches Nordic larp involves physically or psychologically difficult experiences like simulated prison camps which you generally don’t see in improv.
I do love that it’s a hobby which sometimes leaves you asking “why do we do this to ourselves?” But these kind of experiences can have a powerful impact. A great example would be the larp Brud Pris about which everyone says “it was an absolutely awful experience/it changed how I see the world/ you should definitely play it.”
I don’t mean to leave you with the impression that Nordic larp is an unsafe activity. In fact I feel that roleplaying games have a stronger safety culture than improv. I plan to write something about this soon.