So since I know most of info from Codex already I can share my initial impression on units we have access to:
Wall of text incoming.
Troops :
Cultists - well what is 4 point
ppm and is troop choice - can never be bad in first place. Nothing much to add there. If you want Battalion
CPs bonus , but don't want to invest much into Troops but some other stuff - this is hands down best choice.
Plaguebearers - marvelous statline, probably best tarpit around per point invested. But there are few problems. No
DG keyword alone is solid issue and fact that you can't field them right of the bat , but only summon them unless you want to lose legion trait (if understand correctly). If they had
DG keyword - hands down best.
Poxwalkers - Some people love them, some hate them(me) - nowhere as cheap as cultists/conscripts and at same time nowhere near as resilient as similar value models (plaguebearers). On top of that very unimpressive statline especially offensive part - makes them also inferior in terms of damage output to stuff like Ork Boys.
On top of that they are notoriously slow unit that in order to be of any use other than holding objective they need VERY EXPENSIVE support characters - Typhus/Noxious blightbringer and possibly other new elite units.
Still valuable as 10 man tax that can hold objective without running way through morale.
Nurglings - nothing new about those buggers - they share similiar issue with plaguebearers. If want them better take another daemon detachment.
Plague Marines - I used to think they are very overpriced. Now I still think they are. But there are ways to make them work and get your points invested back. As long range support they are surprisingly deadly if you invest into special weapons and resilient at same time.
As
CC they can still dish as yet another surprise staggering amount of shooting damage via grenade stratagem and some other support.
Still more reliable as shooting. Wouldn't really take
CC option as we have better
CC stuff to get the job done.
Final verdict - Average choice. Not as bad as I used to think.
Affected by crapton of various buffs, and they benefit from them all.
Elite :
Possessed - no thanks. I mean they are not horrible, but they don't really get anything from
DG tactics except for some cloud of flies stratagem. Average at best. And we got tons of Elite picks and some are very strong.
Helbrute - well not that bad and it actually benefits big time from Legion trait - it can move and shoot twin lascannon and still close in to
CC with scourge/fist.
Not bad, but got too strong competition out there. Competition that may not hit as hard , but is much more durable/flexible.
Blightlords - everything is good about them. They may be what other terminators wish to be. Actually tanky and they don't like flies to very popular plasma or smite mortal wounds.
Powerhouse in both
CC and very solid as shooting support - can rapid fire plasma / combi bolters up to 18" after deep strike. No weak spots, not overpriced at all. Actually steal.
Slow , but 4+ invu is worth it. Top pick.
Deathshroud - I love those guys by default. But seems they are not as good as I wish them to be. 75 points per model - you can get foul blightspawn/other elite dudes for this point value of single model. Very deadly once they get into
CC range. But if they don't ... they act as very expensive meatshield for characters - that is if there are any around and they can keep up (probably not).
And chances they won't make into
CC are sadly very high.
If you take Land Raider - they are excellent. If you don't - average if not worse. Land Raider can help them get guaranteed charge - and they can really hurt a lot. Thier value as meatshield is also questionable at best ... they are 75 points each - do you want to save your tallyman there. Or actually save deathshroud more ... Not easy choice considering point value.
Foul Blightspawn - That dude is GOD, his flamer alone is worth it. This thing can wipe out entire custodes units with some good rolls. Other skills make me want to take 2 of them. Top pick.
Biologus Putrifier - Not as good as guy above, actually much worse. But not entirely worthless either - can achieve spectacular effects if he accompany
CC plague marines in Rhino. Grenade stratagem and his ability can dish insane damage with plague marines jumping out of Rhino to throw some sweets. More of cheesy situational guy, not bad though - average.
Noxious Blightbringer - we know this guy.Vary from autopick to not welcome. Autopick for armies who need to advance fast to
CC/flamer range. Not welcome to armies more oriented around slow advance and shooting/ stationary gunline. But very useful for infantry based army. Good choice most of the time.
Tallyman - Hmmmmmmmmmmm ... not sure about him. His
CP cheese is not actually bad and basically 6
CPs are worth on average 7 with him. So that alone ain't half bad. His other ability is very potent in
CC. He is okay, depending if he can keep up with said
CC units.
Why I don't value him higher ? You probably have Daemon Prince rerolling 1's around in both shooting /
CC - and Prince is doing tons of other stuff aswell. Mortarion himself also gives such aura. And Morty will be in front of your lines in same area where you want your tallyman.
That being said - if you don't take Morty - then yeah he is good and only 60 points + 7 for pistol. So quiet cheap.
Surgeon - Sadly very unimpressive dude. Eats on VERY CROWDED Elite choice. His only notable skill is rerolling 1's on
FNP - that is garbage. So extra 5,5% to pass
FNP test. Sorry not enough to justify taking elite slot and his points. Although he jumps to Average choice against Space Marines thanks to his other ability.
Fast attack :
Foetid Bloat Drone - Unquestionable MVP - when everything with few exceptions is slow in our army - they are daemons of speed. Able to move up to 16" and still shoot . Resilience wise they are fantastic. Flexible with weapons - can perform various roles and in fact perform all of them pretty damn well. And that is still not all they have - they benefit heavily from Mortarion auras and are his true companions - not slowass deathshroud. They love all buffs he provides , they can advance with him and provide support he needs so badly. Last but not least it's impossible to render them useless via
CC. Fly rule gives them possibility to disengage and shoot more.
CC variant want to be stuck in
CC anyway. Easily must have in great numbers.
Myphitic Blight Hauler - not as good as glorious Bloat drone - but still good. Except for Bloat drones - not much competition in Fast attack slot , so they probably gonna see table a lot. Especially that you can take them in units of 1-3. So All they need is just 1 fast attack slot - and they deserve it.
Fast anti tank support for our army that benefits a lot from getting 3 of them. Demon Engine that after moving 10" can shoot and hit at 3+ , with morty around at 3+ rerolling 1's ? Pretty neat and deadly. They also provide very powerful buff to your Plague Marines, may be in fact one of best buffs for our Marine squads. 2+ terminator armor , damn. Useless for poxwalkers etc 6+ won't last long against any
AP and even without won't save many.
Now to the weak spots : if you don't take 3 - it hits with 2 weapons at 4+ and costs around 137 points. Average in
CC and additional assault weapon while nice - unreliable and low range. But weakest spot is lack of weapon costumization for this unit. Only Melta + Missile Launcher - 2 weapons I would not rather have in fact I wish i could take Entrophy cannon/plague spitters/heavy blight launchers there. Not saying it's weapons are useless, but there are better ones that we cannot take. And unit of 3 costs more than 400 points ...
Plague Drones - no
DG keyword but good as summoning unit. Cheap for what they do, 102 points for 3 very tough and fast tarpit units - seems like deal I like. They can also do some damage rerolling all wounds despite no
AP.
Chaos spawn - actually very strong choice despite serious competition from drones - since you also can take those in units of more than 1. So not taking too many slots. And damn those things can be deadly once they get into
CC. Per points invested - i dare to say they are also durable. Yet very vulnerable to multi damage weapons.
HQ :
Lord of Contagion - now we can talk. Idk how much Plaguereaper costs, but since we can use Manreaper - it's irrelevant. He costs as of now 120 points + 17 for manrepaer - 137 is not 184 he used to be. As I expected we got him for ~~50 points less.
Sadly his movement is pathethic and he relies on either Land Raider or lucky charge from teleport strike. He can't cast any powers, his aura is garbage and he doesn't shoot anything , not even grenades
lol.
But now with reduced cost seems like he can at least justify his place on board as anti-elite infantry , character stuff. He is also pretty durable and with archcontaminator - if you don't have morty on field - can actually be of any use to others. In that case take relic for extra 3" range.
And suddenly he is better archcontaminator than Mortarion himself !! With 10" bubble for wound rerolls on plague weapons and 10" aura for his less useful chance for mortal wounds.
Still kinda meh, but again if you don't have Morty - and typhus can't take Archcontaminator ! Daemon Prince don't like archcontaminator either as he don't swing plague weapons himself.
Typhus - very good pick, but just don't make him warlord - sadly he ends up with pretty unimpressive if not straight worst warlord trait. But still excellent choice as
HQ - combines psyker and lord contagion in one. Also buffs Pox and got GOD tier
CC weapon on top of cool pistol.
Autopick.
Malignant Plaguecaster - solid psyker , very impressive if you can get him close to opponents. Sadly his job can be done by typhus/mortarion and even Daemon Prince to some extent. Thus he may not see field too much. But that is just strong competition - he is still solid.
Daemon Prince - with wings or not - still insanely fast for Nurgle Standards. Insanely resilient , very potent in
CC, psyker, powerful reroll aura. Access to awesome relics he likes. Along with Typhus your
HQ beast.
Lord/Terminator Lord - useless except for budget 1's reroll. Thus may see some use if you drop him with Blightlords. Except for that - hard to justify him.
Sorcerer/ terminator Sorcerer - pointless - if you take Sorcerer - you are better off with Malignant dude thanks to his 7" deadzone. Terminator option pointless thanks to Typhus. No warptime ... so yeah.
Lord of War : Morty - worth his points ... but not mandatory. 470 is a lot - you can get crapton of stuff for it. Worth it if you can build army that can support him / advance with him. In any other case - not so much actually.
Heavy support :
Plagueburst crawler - who said we need to advance because we can't shoot - Now this thing is cheap, deadly and looks good on top of that. Heavy firepower support , no longer we miss Forgefiend or Havocs - though obliterators yes

. Very good pick in fact best in Heavy slot.
Insanely tanky rivals Land Raider in this aspect and costs less than half !
Land Raider - same old Land Raider everyone has. I wouldn't take it - unless I will run Deathshroud/Lord of Contagion - those guys need reliable ride to do thier job. Situational.
Predator - if not Plagueburst Crawler ... Well here is alternative take - if you have Morty - then this Predator probably won't get nuked , so in fact it may live to shoot itself. And with BS3+ and 4 lascannons - at 48" it's our best
AT choice actually. But then again once they start shooting it - won't survive too long.
PBC beats it.
Defiler - only real competition for
PBC - also pretty durable, regenerates, also powerful at shooting and equally/more deadly in
CC. If you have one - field it. No Daemon Engine stratagem really hurts this crab a lot.
I hope I did not miss anything

.
Please consider those are just my oppinions and you are free to disagree.