Why do You guys believe that FromSoftware is so popular/Successful? What makes their Boss and Environment designs so impactful.

The reason I asked this question is that currently I am working on a concept art project for my College course. Where my project brief is to design some 2 Humanoid bosses, a Creature design for another boss and a Environment design for a hypothetical FromSoftware Game based on Mayan Mythology. Where the Deities are corrupted by an Eldritch Entity.

One of the requirements for this project are audience research. But I am mainly posting this as I want to know your opinion on what makes their games special so that I can potentially incorporate these elements into my designs.