This could be slightly early since the thread's not officially closed, but there's enough to comment on. As you noticed, I kind of checked out of this one, and I'd like to apologize but reading back through it, I still get the same feeling. Normally a collab is two or more people who have a story in mind and are writing it together -- there's a clear objective and purpose tying the turns together. In the TWFNE story, Fin took more of a dungeon-master role, where he is leading the party on an adventure -- and the key there is 'leading.'
This is how a lot of PM threads are run, and generally it's made clear what the players are doing while the DM writer reveals new details to keep the plot going, or encourages players out-of-game to take certain actions or focus on particular details. There's still interactivity, even though much of the plot is hidden. The goal is, in fact, to reveal the hidden details not to lock them away.
The TWFNE threads really suffered from a lack of direction. Starting out, a mystery and emergency is established, then there's the big battle with the guard outside, granting a brief tease at the plot. After that, though, there plot seemed to disappear into the background. The puzzles kept us entertained out-of-game and I applaud the idea behind them, but from a reader's perspective there was little weight in the solving, and that lets down the writing. Combat encounters were, no pun intended, pretty lifeless in the earlier sections; I understand, you don't have much of a passion for writing combat. It was a good step to bring in Arun for the next part -- which started out as a fun boss battle before communications went sour. However, as far as I know, Arun wasn't given any plot knowledge and so couldn't add weight to the encounter. We don't know who we're fighting or why, just that they're an obstacle to overcome.
I can see that plot details did finally get revealed, but I feel like it's really a case of 'too little, too late.' That's a shame because I normally love this sort of thing, with players adding to the greater lore of the world. This gives us a glimpse into the final moments of an empire... which we've never heard of and seemingly will never hear from again. Moon and Myst put in a lot of work trying to carry this ending by themselves, and I feel like they did a fantastic job with what they were given, but the greater impact is lost because we weren't given anything to invest in. We didn't get to see the princess enough to know whether to admire her efforts or scorn her hubris. There was no lesson to take out of the story.
All the elements of a good story are here, it just never really came together, I suppose. At least part of it may be my fault, but I genuinely don't know where else I could have taken things with Keydis.