There are definitely spin-offs that stick with me through the years, though!
I'm not quite sure how to put into words the element that makes me like these spin-offs. There's a certain camaraderie between the agents, I think: a casual friendliness that makes me feel that they would all be close, caring buddies, even in a more "normal" setting. I guess I like that found family element? Again, I'm having trouble putting it into words, beyond "I like the way these characters speak to and interact with each other."
Miah made a fairly long spin-off, and it was even better before Caddy-Shack's stuff fell off the internet, since they did a lot of crossover work, but it's still quite a project of long-running character interactions.
Rez's agents are just super fun to read, and I like the structure of the missions, too!
And Makari's series is a bit short, but the characters make it worth it, especially considering the twist at the end of the final mission . . .
—doctorlit was going to bring up Caddy-Shack and Ellipsis Flood as well, but it seems their works are missing from the web. He has backups, but won't have time to rehost anything any time soon . . .