I'd like to start routing this, but I need to figure out the rules first. What do you think the criteria for a good ending would be? I'm thinking it would be based on the movie at the end - obtaining the best (or one of the best) texts for each shown slide.

From looking at the WoL wiki, I think the criteria would be
1. Complete the main quest with whatever's fastest
2. Fill Dirtwater with 4 shops (4-6 makes Dirtwater a thriving metropolis)
3. Trap Duke Bovinicus without being Cowrrupted
4. Seal Roberto

There are several other slides that CAN be shown, depending on circumstances, so the run would also need to avoid situations that add to the slideshow unless what you're adding is also positive (like Buffalo Bufallo Buffalo Bill opening his restaurant). Since it's based off of the slideshow, ending would be at the end of the slideshow, which would also encourage avoiding sidequests.

What do you think of this definition? Is there anything that you would add? Does it sound OK to make a good ending that doesn't include helping all of the optional NPCs?

I think it could be a good idea, I'm not super well-versed in the slideshow since I usually ignore it/skip it, but I do remember a few base "endings" being shown in an any% run, imo I'd classify a "good" ending as all of the base slide endings being positive when shown, and then a possible 2nd category depending on how many additional slides can be added, "best" ending, which would be all base slides plus all positive optional slides added as well, maybe "all ending slides" if there's some always negative ones as well. I am garbage at routing, but submitting a run will most likely get better attention from the mods even if its not optimized at all

Thanks! I'll try it. I'm using the wiki link (https://westofloathing.fandom.com/wiki/Ending) to pick out what's optional vs. not. Looks like it's going to be
1. Clear the main quest, and specifically DON'T build the bridge from Breadwood (would count as solving one of Breadwood's problems, which would mean needing to solve all 7 for the credits)
2. Put 4 shops in Dirtwater to turn it into a thriving metropolis. Will probably add getting the inn room as a requirement so you see the text about getting a plaque
3. Finish the El Vibrato questline by sealing Roberto
4. Trap Duke Bovinicus and don't have Cowrruption perk at end

Looking forward to routing this and trying it!