Today has been less about the models for me and more about the game and how the Daemons work within it. I've only been able to do this with 40k at the minute because I don't have a WHFB rule book yet.
This thinking came about while I was creating a data file for Battlescribe because there isn't one that I've found yet. I was working on the Heralds (convincing that programme that 4 Heralds are allowed to take one HQ slot was tricky but I've managed it) when I started to think about the best way for this army to function and after some careful thought I've come to two conclusions. The first is that my initial feeling was wrong and that this is NOT a hoard army. It's not exactly a "lets field 5 warriors per unit and still kick ass" army but it's not throwing millions of units at a problem and hoping to overwhelm with sheer numbers either. I'm now thinking that this army is actually somewhere in the middle in that you can still field pretty large units but flooding the battlefield (a la Tyranids) would be way too expensive (in points and pounds). To me the basic army setup is big units that play to the strengths of the factions (i.e. utilising Slannesh's speed, Khorne's strength, Nurgle's resilience and Tzeentch's range). Of course they've added other effects to the units that change how they can be played and to what use each unit is put to but I'll review each unit at a later date.
The second thing I realised about this army is that each and every unit has the Deep Strike rule but that Daemonic Assault is gone (the way I understand it, that rule involved splitting the army in two and letting Fateweaver decide which gets deployed and which Deep Strikes). Now there are two things that can be done with this information; one is that it can be ignored completely and the other is that it can be incorporated and utilised. I haven't had a chance to play the new rules yet but it looks like the first option isn't the best one as the saves in this army aren't great (in fact they kinda suck even if they can be taken against pretty much everything) so then the question becomes how do you strategise around something as random as Deep Striking? As is so common in this Codex the answer is two-fold; Icons and Instruments. Icons stop units from scattering and instruments let you bring in an extra reserves unit for free if it's of the same alignment. The most obvious way I see to incorporate this is with fast moving units with Icons deployed normally, get them as close as possible without dying, bring in units with Instruments and/or more Icons then bring in units that don't have either as the free unit. An example being to use a unit of Seekers (move 12", Run an extra 6" thanks to Slaanesh) with an Icon to bring in a unit of Horrors with at least an Instrument and use that to bring in a unit of Flamers or Screamers. If you place them right then you can get the Flamers or Screamers up to 12" closer to the enemy and in a better position to rain down a lot of hurt than if you tried to get them across the battlefield individually.
I'm sure that there are a lot more combinations but that use of Deep Strike has the potential to keep your high damage but fragile units safe until they can be put in a position to cause maximum carnage. The downside to this strategy is that if the first unit is killed before you can utilise the Icon then you're stuck with your hard hitting units being thrown all over the place by the Scatter dice which makes it very difficult to effectively strategise or do anything at all other than panic.
I think the most effective way to use this army is to really get a handle on the rules it creates and learn how to use them together to throw off an opponent, such as Deep Striking some Fiends of Slaanesh (with their anti-psyker properties) right in the middle of a Grey Knight army or dropping a big unit of practically indestructible Plaguebearers on top of an objective. Even bringing in some Flamers against a hoard army would cause a lot of havoc if placed correctly.
The point I'm trying to make is that although the rules have changed and the army has become a little trickier (thank you very much Warp Storm table <.<) it can still be a very powerful army with a LOT of firepower behind it if you can be an inventive strategist which, after all, is what this hobby is all about.