RM wrote a LOT of good fiction, some of it slightly fanfic, some not.
I first met him online in the early 1990s on one of the Usenet boards, which was dedicated to "roleplay" via stories.
He continued writing even up to the accident. Here's a (large-ish) collection of his work, solo and in collaboration with other writers.
It's a "shared universe" thing, so note that one or two of the other were less skilled or had a different take on things.
https://shifti.org/wiki/FreeRIDErs_(setting) One of the starting places.