Finally making my way back to the series I started on the way to Seattle - designing a setting. Several people made very useful comments on the introductory post, and I'll pick up on those in the inevitable articles that happen after the one's I've planned :D
Not taking things in quite the order I listed them at the start, we'll begin with:
Fluff. Fluff is that stuff that isn't essential to your setting in terms of rules, army lists etc. The peripheral writing, the backstory, the art, you name it...You can play in your setting without it...
...well, actually you can't.
Ok. You can. But all you're doing at that point is pitting two sets of statted up miniatures against each other and having a battle.
The best settings, the ones that draw you in, are the ones where the fluff grabs you and draws you in, inspires you. It's the stuff that gets you immersed in the setting, wanting to be a part of it.
Let me give you a couple of examples.
Like or loathe the business practices behind it, the Warhammer 40K universe absolutely rolls in fluff on an epic (see what I did there? :D) scale. It might not be your cup of tea, but I guarantee you that it wouldn't sell half as well if people didn't like the backstory.
On a more personal note - I adore the pre- and early Clans setting of Battletech, and all its history. Two particular bits of its story grabbed me - one was the character of "Snow Fire" (after which one of my character's 'Mech's got named), the other the mercenary unit the 12th Vegan Rangers. The latter scored at least in part because it wasn't as well-fleshed out as the more 'famous' units in terms of having books written about it (See? whole books! Fluff! And THEN some!), while having enough tantalising hints dropped to draw me (and a number of other players) in and want to create more in the setting. (We'll come on to sub-creation and open-endedness later in the series.)
And a question: those of you who read this blog and play or intend to play Dux Brit. How much have Andy and my campaign narratives helped to draw you in? (Dux Brit has some other features, setting and campaign wise, that we'll discuss later, but for now... :D)
 I'm 20 years the better writer since that story was written. Be gentle :D