The good:
the location is fantastic, literally a few steps from the Duomo, any closer to the Duomo you would be inside it. The (small) lobby looks good. The staff are courteous and smiling, if not exactly falling over themselves to help customers. The room was very clean.
The bad:
My room had all the gadgets (CD player, DVD player, small flat-screen TV), but was really quite small. OK, it was a single room, but in a five-star hotel I would expect a larger one. No room to swing a cat here, very cramped. The corridors were a bit dirty, and the finishes in the corridors were quite cheap, basically walls made of grey plastic.
The staff's English was so-so (just about acceptable in a five-star hotel); problem is the staff's ITALIAN wasn't very good either, which I find puzzling and unacceptable for a Milan hotel! I guess most of the staff were Eastern Europeans. But as I said, at least they were smiling and they were polite.
The breakfast buffet was definitely poor by five-star standards. Furthermore, the buffet was lit by a multicoloured light (the room has no natural lighting), so I couldn't tell if the food was fresh or not, because the croissants looked bright red, the milk looked bright blue, etc...
Ultimately though (although this is not inherently the Gray's fault) this hotel suffers from what I call The Tiny Five-Star Hotel Syndrome.
The Gray is very small. Call it bijou if you want, I call it tiny. When a high-class hotel is so small, what CAN it offer, apart from good service, cleanliness and a few gadgets?? There is nothing here.
Maybe I am old fashioned, but to me the mention of a five-star hotel evokes the idea of large elegant communal spaces, gardens, terraces, balconies, a pool, a spa.
A Very Small Hotel, no matter how you doll it up and no matter how smiley the staff are, remains a Very Small Hotel. But I guess that for some people that is a good thing.