This was our favourite restaurant in Beijing (we visited Beijing in September 2014). The food is really great and the prices are reasonable.
The menu contains lots of different dishes and it has pictures for each dish.
The location is very central (near Wangfujing) and with the HappyCow map and description it is easy to find: Find the shopping mall with the Apple store at the front, walk west through the night market and turn right at the end of the street. Then right again and you see the restaurant at the right side of the street after walking a few meters.
Tip: Order the Beijing "Duck" for 68 RMB (2 persons).