Followed immediately by ...
How can people who love the fantastic rather than prosaic find happiness in a rules system?
I don't have a comprehensive answer right now but here are a few tidbits that tend to push rules to the "fantastic" rather than "prosaic" side.
- In 1st edition AD&D, the artifact descriptions with their powers intentionally left blank and to be filled in.
- Any system that replaces mechanistic magic with animistic magic ... where social interactions with magical entities replace mere point-and-fire. Stormbringer's demons, Legend of the Five Rings' elemental kami, and Goodman's Dungeon Crawl Classics with its sorcerous patrons all come to mind.
- The Birthright idea to have mythological monsters like the Chimera or Medusa be hugely powerful one-offs, as in actual Greek mythology, rather than whole species (let alone with an "ecology.")