The runner I talked with is a group runners with the store who has run in the Ghost 8 and previous Ghost models. When he heard we had the 9 he came to the store to try it out.
The next part of the shoe that he liked very much was how it felt in the arch. he said it was exactly where it is supposed to be. The last specific part of the shoe that he liked was the heel cushion, again just that it was real nice and better than the Ghost 9.
I don't want you to get the wrong idea, this runner does not just like every shoe he puts on. He is critical when need be, he got a pair of Brooks Neuro and did not like those. So long story short, the Ghost 9 seems to hit all the sweet spots. People that have tried it on in the store have said great things as well.
Visually some of the things you can see about the shoe is a differently shaped toe cap which some have said has given extra toe space. The treads on the outsole are pretty similar, just some slight variations. The forefoot is missing some overlays from the upper which runners I have talked to liked saying it give more forefoot space and helps the flex on the upper mesh.