I also posted this on DH forums, but as new codex has both Grey Knights and all three major Ordos it belongs here, too.
Okay, I happen to have access to large parts of the GWs Grey Knight codex which will be released in April. Now having read through it there are few interesting lore implications, some of which match FFGs stuff, some of which dont:
Temple Assassins
Did you really, really think the Grey Knights are the most powerfull beings Imperium has? Think again. The Temple Assassins are it. Really. The new statline puts the Temple Assassins well above any Space Marine ever existed. Hell, they can kinck Grey Knight Grand Master into curb and not get tired. And no, we are not talking about "minor scaling" things, we are talking about WS/BS8 against WS/BS 6 and I7 against I5 when the other statline is same. and this doesn't even take into account what Assassin special rules and wargear does...
Now for fluff perspective this puts TAs where they should be. You need to kill someone? Anyone? Even Horus? Yes, these are the guys who actually have a working chance of success. For the Marine fanboys, well, it just means your favorites are no longer the "Biggest, Baddest Boys Around"...
Oh, the book does include Death Cult assassins. They are just normal human with power weapons, a dodge save and little better WS and S. Comparing to TAs they are just babies with plastic forks.
Daemontech
Yes. Radical Inquisitors use Daemonweapons... But so do the less radical Grey Knights. As they are (seemingly) completely immune to chaos and corruption they can do so with very little risk. Inquisitors have the choice of fielding daemonhosts in their retinue. Pretty much in line with FFG fluff for Inquisitors part, might offend some old-school GK fans.
Xenotech
Now its official. Imperium uses Xenotech in HUGE amounts. And when I say huge, I mean it. The wargear section for both Inquisitors and Grey Knights is literally filled with stuff thats taken from Xenos and not all of it come from Jokaero. Rad grenades, Pyschotropes, Null Rods, graviton guns, digital weapons, xenopoisons... you name it, they USE it. And no, its not "implicated to be xenotech". Many of these items are directly told to be xenotech. Inquisitors can also field Jokaero techs in their retinue to pimp their weapons.
I think this is completely in line with FFG and earlier GW fluff, but once again might offend marine fanboys.
Needlers
This is interesting. GK codex has needler pistols available for Inquisitors, but these things are far from FFGs baby-toy needlers... And this isn't just a "minor scaling issue" again. Its a whole different beast. Needlepistols kill stuff. Seriously kill stuff. They fire hypertoxic monofilaments and are capable of piercing a Terminator armor and wounding even the biggest and toughest creatures (poisoned 2+, for those who know what it means in TT).
Bolters
Nothing new here. Boltguns and Stormbolters for Marines and humans are still same in statline and described to be same beasts. Normal humans still carry both boltguns and stormbolters without power armor to assist in wielding the weapojns. However, there is very little information outside a single sentence ("signature weapon of Astartes, also used by Inquisitor henchmen") so the FFGs version of Astartes using real boltguns and norrmal humans using baby-guns is still plausible. Hiowever, what IS new is one more new bolt type. Grey Knights have anti-psychic bolts which do nasty things to daemons and such. Supposedly these can not be used from normal boltgun.