Good quality hotel of international standard. Modern and well maintained, but lacking much Chinese influence, so you could be almost anywhere in the World.
I'd booked a twin room on a Club floor for four nights, and at the Club reception was upgraded to a Club King bedded suite at no extra cost. The staff in the Club Room were exceptional, and simply couldn't do enough for you, making you feel a valued guest. I don't eat a large breakfast, so took advantage of the breakfast in the Club Room, which offers an abbreviated menu/choice compared with the main restaurant downstairs, but it is of good quality and, again, served by the attentive and helpful staff. That is not to say that the staff elsewhere in the hotel were not of a very high standard.
I suppose the only downside is that the Sofitel is not close to the main attractions in Xi'an, but I'd still recommend it.