On the first leg, in Beijing, we stayed at the Beijing Sihe Hotel, and it was simply fantastic. The room was large and very nicely furnished and decorated in a traditional Chinese style, and the courtyard setting (down one of the old Hutongs just a little east of the city centre) was great - very quiet and tranquil, you could forget that you were in the middle of a huge and busy city. Also, the staff there were very helpful with directions and making arrangements for us, and the meal we had there one night was delicious too. Finally, it was a convenient location - not too far to the nearest subway station, and reasonable walking distance to Wangfujing St (one of the main shopping streets).
If/when we go back to Beijing one day, we'll definitely try to stay there again.
Second hotel was in Xi'an, the Belltower. This was nice, but ... it was just a hotel, and the dinner buffet was a bit ordinary.
But then we moved on to Shanghai, staying at The Bund Hotel. We were in an Executive room there, normally pretty pricey, but it was a reasonable rate thanks to one of the last minute hotel booking sites, and what a room - on the 21st floor, great views over part of the city, and the bathroom was huge, shiny and luxurious. Service was very good here, too, and we had good meals at two of the in-hotel restaurants.
And finally, back to Beijing, and the Dream Castle hotel. We were originally aiming to go to a different hotel, but they apparently had some issue with their rooms and transferred us here. They were reasonably convenient for the Olympics (although in retrospect, somewhere further away, but closer to a subway station would have been better), but really they were more of hostel-gone-upmarket - fairly basic room, and not as much service. Also very thin walls, and a bar/dining/lounge room down the corridor which often had noisy people in it.