Grey Knights, a lot to say.

Ok, this is a cool book, with beautiful new plastic models.

Alright, Purifiers are badass, Crowe blows. Dilemma. He is neither an IC nor an upgrade character, so he is a single model unit with a great model. Ugh. He is essentially a 150 point awesome tax to get Purifiers as troops and make a whole army of them. Worth it I think. But for him as a unit I have no idea what one would do. I guess just run him along behind and hope he can get into combat and not get charged.

However, my first list and thoughts were lots of terminators, no gimmicks or tricks like I have been seeing, just lots of grey knight terminators. Oh hell yes.

HQ

225 Grand master, blind, rad ,MC psycannon 

200 Librarian, shrouding , might of titan , summoning , sanctuary, warp rift, MC halberd, 3 servo skulls 

Troops

475 10 terminators , 2 psycannons , 3 hammers, 1 MC hammer 5 6 halberds, psybolt ammo 

475 10 terminators , 2 psycannons, 3 hammers, 1 MC hammer 5 6 halberds, psybolt ammo

475 10 terminators , 2 psycannons, 3 hammers, 1 MC hammer 5 6 halberds, psybolt ammo

Ok, actually there are tons of  tricks and weird crap in here. I think grey knights HQs have the most weird cool fuck yous per capita of any army. 

Grand Master

On the GM, he reduces enemy Toughness by 1 when charging or charged, also when charged negates the +1 attack, charge me I dare you. Also, his 4 shot psycannon with one re-roll to hit. Also, why keep his normal weapon when he can get a thunder hammer or In 7? A 3++ save in close combat that's why. I have heard people being sad that only one Special Character gets a storm shield. Well, for no additional cost the GM has a 2+ and 3++ in close combat, and with hammer hand, Str 5. 

Oh and Grand Strategy. So with only 3 total units(6 scoring units if they combat squad), from 1/3 to the entire army benefits from this rule.  They are all scoring to begin with, so we have the options to make them Scouts, give everyone Counter-Charge, or re-roll all 1's to wound shooting and combat. 

Not to mention Psychic Communion, with a psychic test any reserve roll can be modified +1 or -1 AFTER the roll has been made. Scout his unit up farther into cover, have the servo skulls(discussed infra) reduce scatter for the other units, and blast the crap out of something. 

Librarian

Ok, the librarian. He can cast two powers per turn. This means your turn and my turn. Hammerhand, Sanctuary, and The Shrouding are all used in your opponents turn. Holy Synergy Batman! Slow down assaults/ kill models with dangerous terrain, give yourself and units within 6in a 3+ cover save, increase strength, all in the other players turn. 

During your own turn the fun starts. Summoning, you take a unit and deep strike them within 6in of you, get a unit where they are needed. Might of Titan, Str 6, when stacked with Hammer hand from the unit you are joined to. So In 6 models with Str 6, force weapons. Again, you go before basically everything but dark eldar characters, wound anything but MC's on a 2+, ignore armor and a force weapon if need be. Also, Str 10 thunder hammers, that are force weapons to back things up. He gets to re-roll a missed attack, so making those force weapons count. Also a JoWW flamer, sweet. 

Now servo skulls, these are another dirty trick that the knights have. These stop infiltrators from being deployed within 12in, and a scout move cannot end within 12 in. So those Baals were planning on getting up in your face turn 1. You can pretty much shut down that tactic with careful placement of the servo skulls. 

Also, most importantly, deep strikes that happen within 12in of a skull only roll 1d6 to scatter. This would include being summoned as well. Holy crap awesome.  

So with  careful placement you can drop you units when and where you want them between the GM and the skulls, and the Librarian. 

Grey Knights Terminators

Alright, they are the same price as standard terminators, but don't come with a thunder hammer and storm shield. However, for the same 40 points you get thunder hammers or halberds, that are force weapons. If you strike at In 6, with a str 5 or 6 force weapon, that 3++ isn't as essential as with the thunder hammers.
The Justicar can master craft one weapon, so therefore one daemonhammer will always hit. Also, since I really didn't have room for other troops, they all get psybolt ammo for the storm bolters. Mini heavy bolters everywhere, in addition to the psycannons. Going from a 4+ to 3+ to wound on the most common infantry, and a 2+ against T3 is awesome.

Now combat squads are where things get cool. A big ass squad of terminators dropping right where you want them, or getting summoned by a librarian is awesome. But, the real strength is being able to tailor the combat squads to what you need. Two five man terminator squads some in on the same reserve roll, and are affected by the GMs Strategy. You can make them a hardcore beat stick, putting the Justicar and at least one more hammer in the squad. Or They can have both psycannons and blast the crap out of things at 24in, and still rock in combat. Or a nice balanced group of 6 5 man squads.

Weaknesses
No actual anti tank. You have quite a few thunder hammers, that helps, and a lot of ways to get close where you want to be. You also have 7 psycannons, which in the hands of terminators are 24in Str 7, heavy 4 rending shots. So using placement and movement can get you side or even rear shots, popping transports shouldn't be that hard, IF you can get into position. Also, with those side and rear shots, shoot the storm bolters first, str 5 shots can glance AV11, and pen AV10, you get a couple glances in before you bring out the big guns, you might get to stack up weapon destroyed and immobilized to take out the tank.