There are several good restaurants in Kolkata and everyone knows Park Street for that. One of them is Tung Fung. They serve authentic chinese as their main cuisine. One could try the buffet in the afternoon, its economical and tasty. In the night, please avoid the weekends as there is rush, which is natural bt the thing is the waiting time there is very high and that is not because of heavy rush, but because the service turn around time is very high there. I would recommend the Gravy chowmein (veg) with white sause and paneer manchurian (with black bean sauce). do not try the soups, you can try some dimsums as starter. Also, as told avoid the weekends, and if possible do a telephonic reservation. but as we know , bengalees go for dinner unplanned as the way it should be!
As far as the ambience goes, the AC was not that effective in summers, and the chairs are nt that comfortable, but the look and feel is grt. I think the tables are placed very close to each other and privacy is not there, I was able to hear normal conversation from the table next to next to me.