Stayed at Westin Beijing Chaoyang for 5 nights in mid-January, I really enjoyed this modern and elegant hotel. Even for a picky guest like myself (sometimes), I'm totally satisfied with the hotel amenities and services.
Executive lounge located on the highest floor (34/F) is among the best I have been to: a nice selection of drinks, cookies, cakes, chocolates available through the day, both Chinese and European style breakfast are available; a well-prepared light dinner buffet served from 6:00pm to 8:00pm; you also get complimentary morning drink delivered when you asked for morning call.
If you have time, try out the sauna and Jacuzzi. When I used it during the weekday evening time few guests were there, which made the experience more enjoyable and relaxing.
All the staff I spoke with were very friendly, patient and responsive.
Location is perfect, about 20-25 minutes to the airport; subway is right next to the hotel.