I just had lunch at Shang Hai Chinese Cuisine in Roswell. They had a very respectable buffet, but the staff were far beyond any other restaurant I have dined in the Roswell area. Despite the fact that I and two friends showed up for the buffet at 3:30 in the afternoon, they cheerfuly restocked several items that had been past their prime around 3:15. Among these were delicious steamed pot stickers and mongolian beef. If you live in the area and are tired of being served by slacker teenagers who are more concerned about their next smoke break than whether you enjoy your meal, please check them out.
2300 Holcomb Bridge Rd
P.S. The manager told me they do banquets with sushi.