Some time in 2009, I realized I had quite many Daemon Princes, so I thought "buying a couple of Greater Daemons and some lesser Daemons should get me a Daemon army". And so, I bought a Balrog (Bloodthirster), a Keeper of Secrets and some Plague Bearers. I was aiming for a "Daemonzilla" list, comprising of 2 Greater Daemons, 3 squads of 7 plague bearers and 3 Nurgle Daemon Princes. The plan was that the T6 monstrosities would withstand a lot of shooting and survive, making a counter-attack right on enemy armour, thus disabling the enemy's big guns.
In the beginning, I was hearing that Daemons are a very strong army. After seeing every "zilla" list played by others getting crushed to a pulp, I reconsidered. After my 5 first battles (with a newer list, more on that later), I reconsidered even more..!
To begin with, Daemons rely largely on pure luck. And that luck is needed TWICE before you even start fighting or applying tactics; First, the Battlegroups roll; You have to divide your army in 2 "waves". The first wave comes on Turn 1, the rest of the army comes in Reserve. That's fine by me, but, for some completely unknown reason, you have to roll a die, and that happens on a 3+..! On a roll of 1 or 2, the second battlegroup comes first, and the first stays in Reserve!
You can imagine how devastating this can be for the player! Yeah, OK, you can Deep Strike your close combat monsters right in the face of the enemy on Turn 1.
And then you can do nothing for a whole turn. So, as the only option to guarantee survival for most of your units (although they will inevitably be damaged/wounded and some might/will die from concentrated fire) is to put your toughest units on Wave 1. Oops, you rolled 1-2! Your most sensitive units are now on the board, unable to do anything (other than a Run move), and your opponent gets a free turn of shooting on them, and can assault them with his close combat monsters. Bugger..!
The other thing you can do, is to split your army as even as possible. This has the advantage that, no matter what, you will have half of your tough units on the board and so you'll be able to deal some damage no matter what you roll on the Battlegroups die. However, since only half of your army are the "die-hards", the enemy can focus on your big things, since the rest of your army is not a threatening as they are. The rest of your army might take a while to come from Reserves, which, combined with 1 turn of doing nothing, it really sucks having your second Bloodthirster arrive in turn 4, only able to act on Turn 5, or worse, arriving on turn 5 and then "game over"..!
And then, you have the scatter dice. So you don't really land where you want, only 3 out of 9 (or 4 out of 12) units will arrive where you want them. If you got 12 units, one will statistically scatter 12", which means it might land out of the board, on top of an enemy unit, or too far from the enemy.
In my test list, I had 2 Bloodthirsters, 3 squads of 7 Plague Bearers, 2 squads of 4 Blood Crushers and 3 Soul Grinders. I played against Chaos Marines, Blood Angels, Imperial Guard and Space Marines. I won against the first 2 armies, I got crushed by the other two.
My preferred battlegroups were: WAVE 1: Bloodthirsters, Bloodcrushers, 1 Soul Grinder. WAVE 2: Plague Bearers, 2 Soul Grinders.
Against the Imperial Guard, one of my Bloodcrusher squads scattered off the table and was destroyed. As a perfect damage mitigation/head-on assault unit, it was a huge loss for turn 1, I highly use them as damage absorbers (2 wounds each, with different wargear which allows wound allocation) and shock attack troops. The enemy then focused on heavily damaging the other Crusher squad and my Bloodthirsters. By the end of Turn 2, both my Bloodthirsters were dead, as well as the Bloodcrushers and a Soul Grinder, leaving me with 2 Soul Grinders and my Plague Bearers. I turned on the defensive, and managed to lose by only 1-0 on a 4 Objective game (he contested both objectives I was holding, I contested 1 of his with my Soul Grinder and he kept 1 more).
Against the Space Marines, I rolled a "1" on the Battlegroups, so I only had my Plague Bearers and 2 Soul Grinders arriving on Turn 1. One of the Soul Grinders scattered on area terrain and rolled a "1", and was thus Immobilized. My first Bloodthirsters arrived on Turn 2 and one was eradicated by shooting (after blowing up a Vindicator), the other got shot and then assaulted by Thunder Hammer Terminators. My Bloodcrushers arrived on turn 4, and on turn 5 assaulted the enemy, destroying a Scout squad and a 10-man Tactical Squad. Good job for a single turn, but too late to save the game, it stopped on Turn 5 and I lost 5-3 on Kill Points.
Against the Chaos Marines, well, the CSM are a very underpowered codex. I played against a solid Nurgle list (3x7 Chosen, 2x7 Plague Marines, 1 Daemon Prince, 1 Defiler, 1 Vindicator, 3 Obliterators), which I nearly wiped out.
Against the Blood Angels, I scored a solid victory, much due to the fact that Mephiston is easy to kill by someone with Blessing of the Blood God. My opponent played a Deep-Strikish jumper list, so I decided to split my army into even halves, as there was not much firepower on the table to take them down, and I would need to have my second wave coming near my lines to help with his invading jumpers. It all worked fine :)
In conclusion, these are the main problems of Daemons:
1. Battlegroups: It should just be like Drop Pod assault; half the army comes on Turn 1, the rest on Reserves, no "3+ and if you score 1-2 the other half comes first". Not being able to assault and scattering is punishment enough.
2. Deep Strike: Having you whole army scattering 2D6" is too much in my opinion. You have to choose between either arriving too far away from enemies, or risking mishaps. If scattering 2D6", the models should at least be able to move, if not assault outright without moving. There could be a rule like "Scatter 3D6" and may act freely, or scatter 2D6" and may not move but may Run/Fleet and assault, or scatter 1D6" and may do nothing but Run". It's a fair Risk/Benefits ratio in my opinion, it sounds more similar to "disembarking" from a Warp Rift than randomly teleporting.
The codex entries are fine, I can't complain about the units. It's the mechanics which make them suck so badly. Alessio Cavatore said he is proud for making an army that is simple and hard to play. "Hard to play" are also the Dark Eldar, but they are not forced to rely on pure luck. "Hard" means "requiring skill", and random dice rolls are not a skill.
So, as a final conclusion, Daemons are a great alternative to Chaos Marines if you want fluff supporting unit effectiveness, but their randomness makes them just as underpowered compared to the other armies in standard games. The only place where I believe they shine is Planetstrike, and for sure can make Chaos Space Marines much more of a threat as allies in Apocalypse games.