I think a lot of the grey knight models are very cool.
The dreadknight reminds me more of that robot from the matrix, or some sort of anime mech than it does a dreadnought, but that's ok.
The models I really don't care for are the terminators.
It seems like they put their crotches in the wrong place, like their hips are too wide and the crotch is too high up. I don't know, maybe it's just me but it does seem like there's a bit of a proportions change from the plastic termies. And they need more details, like seals and tabards and censures (sp)
I like the power armored GKs, even if GW painted them like a horses@$$.
Also some of the poses on the Power armored ones really make you wonder. The storm bolters are SO HUGE, it's almost impossible for me to believe that they could wield 2 handed weapons. They bolter would just run into their chest and they couldn't really swing back.
They are also holding some demon heads? Aren't demons incorporable (or whatever) wouldn't they just disappear to the warp when they die? That last one is pretty nit-picky, but hey.
I think the worst model they came out with is Driago, don't get me wrong, he's got lots of awesome detail, that I feel is appropriate for a grey knight master, however look how he's standing and holding his sword. Stand up and act that out, and tell me if that's something you don't feel awkward doing. But I guess they can't release models that aren't pointing with power swords and screaming.