So, we come down to it: is the latest codex good? Bad? Broken?
Well, my impressions are that it's not really BROKEN, but it's not really good. Let me define the two.
If the codex was BROKEN, I'd expect Grey Knights armies to dominate the tournament scene and be as widely touted as the Guard leafblower. As it is, the Grey Knights look like they have a punch of powerful but expensive units. Grey Knights armies will be smaller than comparable Space Marine armies, but have more neat tricks. About 1 in 12 times their buffs won't go off, and this increases if the enemy has a Farseer, Librarian, or Hive Tyrant nearby. All in all they're very competitive, even with thier own Deathstar: the Paladins. But broken? No.
The codex is BAD because there are a lot of design ideas that, to me, make this not an update to make Daemonhunters more playable but a book to sell Stormravens. This book is geared toward the old Warmachine 1.0 style of thinking: it's not overpowered if everyone has something overpowered. I really dislike the fact that the Grey Knights NEED the Paladins to balance TH/SS Termies, Nob bikers, and all the other "deathstars" out there. I mentioned in my previous post why I dislike the Stormraven as the ONLY Fast Attack choice, but I want to bring it up again because it's still crap.
I'd also like to talk about the old book. In the old Daemonhunters (and the Witch Hunters) codex, there were two "ideals." Puritan Inquisitors used Grey Knights because they needed muscle to fight daemons specifically. Radicals used Daemonhosts and couldn't use Grey Knights. I always thought Radicals got the short straw, as Grey Knights were MUCH better than Daemonhosts, and the 'hosts were random and didn't do what you wanted. What I would have liked to see is instead of the 3 inquisitors in the HQ choices would be two: Radical Inquisitors and Puritans. Puritans would be able to take Nemesis weapons, certain psychic powers, and be able to be in the same army as Grey Knights. Radicals would have access to Daemon Weapons, a much wider variety of psychic powers including the old MINOR psychic powers, and be in the same list as Daemonhosts.
Further, from the Eisenhorn novels, I'd like to see different LEVELS of Daemonhost. Lower level Daemonhosts would be some kind of combat nightmare, the equivalent of an Assassin. Medium level 'hosts would be like powerful characters, with psychic powers. High level 'hosts would be horrifyingly powerful, BUT run the risk of breaking their wards! There would be a constant struggle between the Inquisitor and the 'host, possibly leading to the 'host model switching sides! Such is the price of gambling with power.
Now, let me say that I do like the 3 Inquisitor entries. Each has a "flavor" that makes them whatever you want to be. Plus, the addition of Ordo Xenos gives not only customization but storytelling options. None of the generic Inquisitors are ultra powerful.
In the end, the Grey Knights codex keeps walking down the road that 5th ed has been going down: becoming even more and more broken. Back in the day when the Dark Angels codex came out, I was JAZZED. It looked like they had a codex design philosophy geared toward balance, ease, and matching the fluff. The current Space Marine codex was similar, but started to diverge from that path. Now with so many codexes with such design in mind, each army has become all about finding combos and exploits instead of making a fun list. I guess I'd better get used to it as it's not going to change any time soon.
...and the Dreadknight is still a stupid name.