So... They're out there now, people know they're coming so I can talk about them.
It's true that the Inquisition and assassins were cut. Assassins are getting their own update (similar to 4E) which will let them end up in any Imperial Army without necessarily taking an Inquisitor and have some cool narrative missions/kill team missions.
But we're not here to talk about Assassins.
Grey Knights are definitely getting "stripped" of a lot of the bloat they had before, not necessarily the stuff they had.
What I mean by that is this codex is C:Grey Knights, and NOT Ordo Malleus.
The focus is on the marines and only the marines. If you want to recreate existing armies, its not difficult you just use the inquisitor codex alongside it.
The special characters as rumored at gone, BUT the relics section lets you effectively portray them (functionally) on the table. This lets people convert to their heart's content without conflict as to what is/is not the right way to represent one character or another.
Unlike space wolves and Orks there is no follow up supplement for Grey Knights. It's all in the book already.
Draigo makes paladins troops, but they have to be 4 or more models or else remain elites.
Things got a little bit cheaper to bring them in line with the new base marine costs.
Librarians still require terminator armor.
Land raiders are dedicated transports for strike squads as well.
Deep striking via teleport got more precise.
Grand strategies are warlord traits.
There are 2 new kits only one of which is a vehicle
Have some very unique rules for when playing against daemons primary. /Both/ armies get buffs (fluff wise because GKs only show up when the situation is super dire)
So to reiterate: book is about the grey knights and nothing else cluttering it.
If you want the old book, just grab codex: inquisition to go with it.
It's not GWs fault that TOs are limiting people to two sources. The design process was that the book was too bloated with choices that had nothing to do with grey knights, thus didn't need to be there.
Does it mean less options? Sort of, if you only have one book, but in return you get a more balanced army that isn't being weighed against the strength of inquisitorial henchmen when considering the potency of "GK troops," allowing for a much stronger book if you wanted to play just knights.
Crowe doesn't make purifiers troops in the traditional way, but he has a formation that's him with 2-6 units of purifiers in transports.
In this formation he gets a bodyguard of the new unit that are based roughly on his "story" per se and is the only way to give him a retinue as he is not normally an independent character.
More will hit the internet soon I'm sure but that's all I can say at the moment.
Now, personally, playing on the fluffy side of things, i like to have inquisitors and henchmen in my Grey knight detachment. Particularly as a vague hand-wave or paltry justification on why approximately 5% of the entire chapter (there are only 666 of them after all) is attacking anything except a vicious Daemon infestation. So i usually point to my kitbashed inquisitor or Coteaz and say "An inquisitor made 'em do it" hell, it's not worse than any other justification offered in canon (or blacklibrary's close-as, anyway).
Now, as has been pointed out, there is absolutely nothing preventing me from fielding a Inq (=II=) allied detachment, as a matter of fact, that actually improves things in my opinion, as that means i can shoehorn in a vendetta, and some MORE anti armour, which is usually where i tend to have a gaping hole in my army.
So a new kit? And a new vehicle? i've heard speculations that it could be something like a taurox, but in keeping with the fluff for the GK (and since it is now PURELY, grey knight, not the entirety of the ordo malleus) the grey knights are Quick reaction forces that have access to the finest that the imperium can provide. So i'd wager an anti flyer or something specifically fast, to let us hit them with our swords.
what i'd want would be, as mentioned, a tank hunting vehicle, but the grey knights have always been intended to go against Daemons or Chaos Marines. And Daemon Engines might have AV but Daemons go with Toughness, so probably something that allows two modes of fire, a rapid fire lawnmower and a focus fire S9 at the most, and i'm not holding my breath for "lance" on that mode of fire. But i'm hoping.
I'm also wagering on a FA. the one unique offer GK gets in FA are interceptors, and they are Quirky (what ho'! a quick jaunt through the warp, off we are, TALLY HO!) but i haven't really seen them used, nor in a competitive nor casual environment, which translates into the SS (strike squad box) goes as purifiers/ordinary troopers, so the box is probably selling well enough, but doth' GW smell a profit to be had here? Probably, and if GW has been safe to do anything as of late, then it is follow the money.
And the assasins are getting an overhaul to their MO as well, it sems we're regressing to 4'th, with a standardized Assassin temple dataslate, i've heard vague murmurs of the assasins getting their own "missions" that will allow additional victory points, but i'd be surprised if anything actually solidified about that.
I'm guessing my Vindicare will continue to serve without distinction. But more about that later.
So there we are, i'm looking forward to this 'dex drop. GK was the first army i picked up, and this will strike pretty close to home. So i'm eager to see what i can rag on next.
Ever vigilant.