Now that preorders are going live I am allowed to write this.
I hate to admit this, but I've had the Codex for a week now. Sadly only had time to play 1 game so far with it.
I'll start with a few favorites new things
Astorath - his axe is back to being +2 strength!
With the bonus to wound making me want to maximize attacks, I think Sanguinor will be a really good choice this codex. Also the ability to leave combat and recharge getting the +1 to wound off again
Librarian Dreads flying are a thing again!
The reroll to wound provide by Lieutenants is great, though I think I am more interested in rerolls to hit.
Sanguinary Guard got cheaper. base cost is now 20. And with Angelus bolters cheaper, that makes the minimum cost per model 35 points.
my favorite I have not seen revealed by GW is Descent of Angels. 2Cp. A unit with jump packs that deep struck that turn charges with 3d6. Not 3d6 drop the lowest. 3d6.
My favorite is the banner for the 5+ FNP.
2 others I like,
Angels Wing, jump pack can reroll charge distance and no overwatch by target.
Hammer of Baal. Thunder hammer but without the -1 to hit penalty.
Heroic bearing. Units within 6 inches automatically pass morale.
+d3 attacks for the psyker and +3 inches charge and advance.
Some things I found disappointing:
Dante is too expensive for what he does I think. I would rather take Astorath or sanguinor and save points.
DC should be better, the +1 to wound on the charge does not make up for not being able to use the 5++ for the banner and that Vanguard are cheaper and can get more attacks with 2 chainswords per model.
Baal predators are actually slightly more expensive (the base cost got cheaper but the Twin linked assault cannon got more expensive)
Don't bother playing a Successor chapter. the only reason to is if you want to use Seth.
I will try to answer questions when I can. And will probably add more information as I think of it.