Hmmm ... from movie making/editing point of view ... I am just wondering, the first 2 or 3 min, is it really necessary to show the various cast/readers convening in the hall, chatting, mingering, then sitting down in a row to start reading their lines ... 

Reason: The expressions/mood captured may not set the tone for what is going to be demanded of in the documentary ... IMHO, there are better ways to feature the cast ... 

I kept your comment in mind, hengcs, but to my count that sequence only lasted a few seconds, so I can't say it served as a distraction for me. Were there better ways to introduce the cast? Perhaps. But there's no right or wrong answer here. 

Since I was well familiar with this tragedy through various books and documentary featurettes, Nanking wasn't as eye-opening or emotionally wrenching an experience for me as it might be for other viewers (I was surprised however by the amount of high quality archival footage the filmmakers were able to assemble), but I do believe that it is an important piece of work which deserves to be seen.