So, a brief exposure and some perusal...and I am, disappointed?
Two things jump out at me. First, and dearest to my heart, my beloved 'Nids have received the final kick to the groin...and they don't even have nads.
This is not an 'oh noes, my army is the suxor' reaction (or 'or GK are sooo OP'). It's simply reality. Entire units wherein EVERY weapon has the FW ability combined with gear that can make the Instant Death effect go off automatically...combined with bonus attacks from the same gear. Yeah, it's bad.
Second, and more significant overall, an easily broken and spammed unit. The Inquisitorial Retinue.
For the meagre cost of a 100pt Special Character (Coteaz, who in and of himself is a good buy regardless) they become troops.
With 5 psykers, two Jakaero weaponsmiths and a Chimera, you produce obscene amounts of mid-range (or longer) strength 7/9 AP 2 fire...coupled with the fire off the Chimera itself. fewer than 200pts per unit of that build type, combined with other build types (storm bolter/storm shield toting dudes and melta/plas spam) and we're starting to see one of the strengths of the IG 'dex bleeding through.
With changes, yes, but still there in even more variable form. Transportable CC units, melta throwaway, and assigned FNP wound soaks.
The potential for abuse OUTSIDE the Grey Knights kind of disappoints me. The fact that competitive lists that are going to come out of this (for the near future, I think) may very well have FEW grey knights...well...is that really Codex Grey Knights?
Now, the pix look awesome. The GK units combine to produce fluffy, boosted, nasty elements that are going to have issues where they should and be strong where they should.
Overall I think that if you play GK you will have fun, fluffy, hardcore play.
If you go to tourney and see your opponent pull out a GK codex, you may just expect to see a great deal of chimera, stormraven and Techmarine spam.
My INITIAL impressions...