If you don't know what Abbadon's Black Crusades are: http://warhammer40k.wikia.com/wiki/Black_Crusade, then there you go.
Every so often, Abbadon gets a wild hair up his ass and decides to invade the Imperium. In 999.M41, his greatest invasion of the Imperium spews forth from the Eye of Terror.
This campaign pits the forces of Order against the forces of Chaos.
Imperial Guard, Grey Knights, Adeptus Sororitas, Space Marines, and Eldar against Chaos Daemons, Chaos Space Marines, and (traitor) Imperial Guard.
I haven't drawn a map on the computer yet, so I'll try to put into words my ideas for the campaign so far. It'll be a fairly linear campaign.
The forces of Chaos land on Cadia, the first battle being at the main planetary space port, as the easiest landing zone.
From there, the invaders either advance on the fortress cities of Cadia, or the survivors of the first landing are driven back across the plain.
Either way, the next phase involves the siege and assault on the Kasrs (those aforementioned Cadian fortress-cities.) There will be three of them, each with a different sort of strategic bonus.
- The first will house the immense Cadian Defence Command Batteries. Control of this city will let you fire (an as yet undetermined number of) artillery bombardments at other tables. They'll probably function a lot like the IG Master of Ordinance guys. It'll be powerful, but with a pretty high chance of scattering. And it won't be game breaking. I'm going through the 3rd, 4th and 5th editon main rulebooks for inspiration, since there used to be rules for Preliminary Bombardments. It might be as simple as a couple of free Basilisk rounds. I had this idea yesterday, so it's all a bit of a work in progress.
- The second will house the Cathedral/Basilica, the center of Imperial worship on Cadia. Unbeknownst to any Cadians now living, it is also on top of one of the greatest of the Pylons dotting the surface (or buried beneath it) on Cadia. As a lynchpin Pylon, it's capture and corruption can allow the deepstriking of Daemons onto the surface of Cadia. (You can't do that before now. If you read the Eisenhorn novels (or one of the articles about the black crusades) you'll know that the mysterious Pylons on Cadia are what have been keeping the spread of the Eye of Terror at bay. It's an active sort of anti-warp defense. A major objective of the entire Black Crusade is the destruction of these pylons to allow the Eye of Terror to spread further, corrupting the physical universe.) The Imperial forces are simply defending their city and cathedral. Troops with LoS to the Cathedral will be stubborn, and within 6" of it, fearless. They might gain Frenzy or Hatred, too. I need to re-read the rules, but think rabid, foaming at the mouth kinds of faith. Chaos will also have some sort of special rules, too. I need to work on this some more.
- The third of these cities is the primary Planetary Defence Center, housing this continent's Orbital Defence Batteries. These massive laser installations will allow the controlling player extra degrees of control over the lower orbitals.
Now, I haven't figured out exactly how we're going to do this, but there will be a mechanism dictating the extent to which each side controls the lower orbits of the planet. If one side or the other has enough control to be decisive, their side will be able to reinforce their overall lists to some extent.
That brings us immediately to Army Lists.
This will sound familiar to Derek, Hilton and Parrott, since I'm basically cribbing it from that one set of campaign rules, but each player will make a list of 5,000-10,000 pts (Haven't decided what level yet.) You will field legal armies from these lists.
When you lose a vehicle or unit from this list, they are Dead. Remove from list. Not available anymore.
If a unit excels in a battle (wipes out an entire unit single handed, captures an objective, that sort of thing,) it gains veteran status. There's a table you roll on and they gain a veteran ability (fearless, move through cover, counter-attack, that sort of thing.) A veteran unit has a 4+ roll at the end of a battle to se if they are Actually dead (or only Mostly dead).
The same goes for named characters, only moreso. A named character 'killed' in a battle sits out the next one, as they are busy 'recovering.'
After the battles for the Cadian Fortress cities (if 2/3 or more are taken by Chaos,) the final battle will be at the heart of the Cadian defence command headquarters. It'll probably be in the middle of a city. If the fortresses hold (again, if at least 2/3 remaind in Imperial hands), the defenders will sally forth and there'll be an Apocalypse battle on the plains of Cadia.
So that's what I've got so far, gang. We'll designate one player from each side as overall commander. (An Abbadon and a Creed.) Extra fun for the imperial sides because nobody has to listen to Creed except other IG players. Sisters of Battle, Inquisition, Grey Knights and Space Marines don't give a shit.
So let me know what y'all think. I've got even more ideas than this, but most of it's scribbled on paper at the moment. So far I've got Me as IG (duh), Jeff as Black Templar, Derek as CSM, and Josh as Traitor Guard/various chaos forces.