So, let's start the Guide again - in 7ed. What's new for Chaos Daemons? Psychic Phase! Now, not only the Tzeentch Psykers can cast normal, but all of them - with new difficulties like multiple Warp Charge powers and enemy's Deny the Witch rolls...
Also, there's a Malefoc lore, which allows the army to conjure new squads even with a pack of Horrors - with only Perils of Warp on a double 6. And the precious spell - Cursed Ground, that affects Daemons... When the whole army consists of Daemons!
So, let's review the army's Special Rules
Daemon of Khorne - the furious charge... Not the grand ability, but it's always good to have better strength. Attacking high toughness dudes, for example, or a good-armoured squads like terminators - to give them loads of save throws.
Daemon of Tzeentch - +3 to ld for Psychic Tests is not so good now, but can save in cause of Perils of Warp. Re-rolls of 1s on save is still a good ability. With a new Jink and Shrouded Special Rules, we can get a dedly covered units. And with Cursed Ground, it's now better chances to make 2+ Invilnerable Saves.
Daemon of Nurgle - Shrouded special rule is good, for example, at the start of the game, standing behind the barricade or the building or simply Jink will grant you 2+ cover save. And it won't become useless in process of the game. Also, the units count as equipped with Defensive Grenades - and now you can throw it, making enemy units Blind in addition to good old no-charge-attacks! But, no running is still disapointing :(
Daemon of Slaanesh - they're fast! An additional run, fleet... Good for you! And all melee attacks are rending, which is pretty scary against Wraithknights, Dreadknights etc...
It's an interesting rule, cause you pass all morale checks, still having the ability to Go to Ground, but it's always a disaster to lose a melee combat...
Death Incarnate - interesting one... But it's important who is a Warlord. A monster or Herald of Slaanesh/Khorne on the Juggernaut with ap2 are the good ones.
Deatroyer of Mortals - a strange one. The most strange to have such, if you play with an army of Khorne with Locus of Fury or Skarbrand.
Herald of Doom - not too useful, I think.
Immortal Commander - a good one, the possibility to avoid a disaster with an Instability.
Lord of Unreality - the best one. Making a negative effect of the Warp Storm almost never...
Warp Beacon - a crappy one... It could be good to know such trait in the moment of roster creation, not before the game has already begun...
So, I think, it would be better to use the Rulebook traits, if your Warlord needs to roll one - Command and Strategic ones.
An unusual feature of an army - something, that can kill unexpected!!! Note, if you have the ability to re-roll the table, it's better to re-roll only the first three results for a maximum safety!
Icon of Chaos
A good one, playing with a Deep Striking units, like the Great Unclean ones. Don't forget to use that ones for the allied CSM - to say hello for Land Raider with Obliterators' meltas, for example! But, the Cursed Ground making this work better - it has a 12" radius and making to "hit" all of the Daemons, not depending of Daemonic Alignment. But, that spell gains with a random rolling, while the Icon is just can be taken in a roster.
Banner of Blood - very tasty one. You just don't have problems with charge and you always know, that you'll make it successfully, if there's 7" to the enemy unit.
Blasted Standart - an additional damage, I don't think that it is necessary.
Plague Banner - strong... But for whom? Plaguebearers are too slow, while Drones can take permanent 3+ poison...
Rapturous Standart - Interesting, but I don't think that necessary...
Instrument of Chaos
The save-points for the Storm-attacks, but you never know which god will attack, so it's not the main ability. It's good for Deep Strike! In the combination with comms-relay it can let you to have on the table the reserve, that you need :3
The Eternal Blade - good one for the monsters, but not so good in 7ed with a new Smash.
The Portalglyph - a troop-creater... Making Horrors and Warp-Charges! If you are lucky enough to roll "6" on the Malefic, it can be a Greater Daemon, heh!
The Doomstone - a strange one stuff. It could be used in a herald-boing, for example. And maybe good with a Slaanesh Psychic lore.
Grimoire of True Names - a favorite toy of a Daemon player! Buffing the main unit in the army, ore one of the important in certain moment of the game. It's better with Kairos! And don't forget that CSM have Daemons too!
A random buff of a Character. I can call it a unique stuff for Daemons. That things can just change your and your enemy's tactic just before the game, as Psychic Powers can.
Daemon Psychic Powers
Discipline of Change
Flickering Fire of Tzeentch - not too bad to have such power. But, it's difficult now to decide, how much Warp Charges to pay - you can not to cast, or, trying to find 1 Charge to have 3 successes...
Tzeentch's Firestorm - the worst power of a lore...
Bolt of Change - a strong one. Even can break a group of Vehicles with a luck.
Infernal Gateway - interesting, but 2 Warp Charges...
Discipline of Plague
Stream of Corruption - I just think, it's great. For a Prince, for example.
Plague Wind - a good one too. Short as a range, but ap2.
Miasma of Pestilence - good for the fights of middle-initiative squads like Khorne units, Screamers, etc. For Nurgle units with low initiative or units with high one, the effect will be only for the WS.
Rancid Visitations - it's weak and costs 2 Warp Charges...
Discipline of Excess
Lash of Slaanesh - not the best power, but it's always good to have that like an additional weapon.
Aquiescence - really the strong power. Blocking the overwatch and making enemy unit to strike at initiative step 1 almost always... Yummy!
Pavane of Slaanesh - just interesting, but won't deal much damage.
Cacophonic Choir - a weak version of Psychic Shriek, that cost 2 Warp Charges...