Well, as much as it truly pains me to say it, stories are not essential to the NESing experience. Trust me, it REALLY hurts to say that. In fact, I feel that rewarding stories with actual gameplay mechanics may well discourage new players or those lacking confidence in their writing. They would feel that they've suffered and unfair disadvantage. Now, it could also be argued that this is hardly the problem of the good writers, who deserve reward for their skilled writing. Personally, I believe that writing should be its own reward, but don't discount this as me saying that all creativity is bad from the player side. As anyone familar with my current and recent NESes, I'm a big fan of army customization. Sure, it can make stats a bit more confusing, but I believe that such efforts of customization can make a nation feel like more of a person's own than it would otherwise. That's just my opinion anyways, which I've noted, as people who get more invested in my NESes are typically the ones who enjoy creating their very own units. I may have that wrong, it's just speculation.
Now, as for what makes an NES good, yes, I've actually read through each and every one of these, not just my own over the past few years. Regardless of what we define success, I believe that if people are saying "I'll try against with another NES, here's the link," "You should post this ruleset on _______ to get comments," or "Shame it died, it had potential," it was NOT a well moderated NES. Instead a good NES typically has comments that are calling for a revival of the NES, a surplus of after the fact stories, or were bumped by a troll/idiot sparking statements along the lines of "I remember this, a great NES." Therefore, based on what I've read, here's the following ingredients for a good NES, based on player reactions over the years, not in any particular order:
1. Moderator interest: and I can't stress this one enough. If the moderator doesn't care about the NES, it WILL show, and players will not join. Furthermore, the one thing I can say, is that regardless of whatever statements the players or moderator makes, the only person to blame for the death of an NES is the moderator. You can cry out personal reasons, lack of player interest, or "temporary" haitus as much as you want, but if the NES dies, the moderator is the only person to blame.
2. Number of updates. In the past, a NES was judged based on how frequent the updates arrived, and most of the time, if an NES didn't receive 3 updates a week or more, it was considered dead. Needless to say, this was a lot of pressure on the quality over quantity strategy. Thankfully, those expectations are long dead, and we can all move forward. Regardless, depending on the type of NES, some NESes require more frequent attention. I'll make an example of my and Milarqui's Tropico NESes or story NESes in general. If those style of NESes are not frequently updated, everyone's interest will wane, and thus we display the inherent flaw in story based NESing. With a stat heavy NES such as CIEN or most other NESes, the player bases typically become more tolerant of long updating times and waits between updates. In these cases, the longer people have to conduct diplomacy between updates the better. In other words, the key to a successful NES is balancing the correct ratio of waiting time to number of people playing in the NES.
3. Don't be Sheep. I mean that in the most literal sense. Take a look at any of Sheep's NESes, do exactly the opposite of him, and you're already 60% of the way to success.
4. Setting: Frankly, ANY setting can make a surprisingly good NES. Once again, this is another sign of how the NESing forum has evolved as a whole. Based on what I read, back in the day, if it wasn't a "Fresh Start" NES, it would die on arrival or shortly thereafter, with a few notable exceptions. I think we have The World Turned Upside Down and the Fall from Heaven NESes to thank for finally putting that expectation to bed. Based on what I've seen, NEVER do an NES where you have to expect all the players to know the background of some other fantasy game/movie series by heart. I've seen so very many DOA Star Wars, Fallout, and so forth NESes. Furthermore, never expect that a good franchise will make a good NES, at least not without a lot of tweaking.