I actually give this documentary 3.5 stars.,,but the reasons i deduct at least 1 1/2 stars is that I think this documentary should have included more cities such as Sao Paulo , Paris, Sydney , Bangkok,, New York, Moscow, Berlin, Mumbai (Bombay) ,etc. This documentary only covers about 5 "mega cities"...:Shanghai, Tokyo, Mexico City, Dhaka (Bangladesh), and London. There is very interesting things to see on each of the 5 mega cities shown in this documentary but seems to focus too much on only certain cities..example Mexico City and Tokyo..although these are interesting to see....It would have been much better if had spread the focus to include at least the top 10 or 15 major cities of the world.
Also I think that it seems a bit too "entertaining" at times.....such as the segment on kidnappers, gangs, bullet proof vests and defensive driving in Mexico City. It kind of goes off into tangents in several places in other cities reviews too and i think these might just would have been better time to show us other major cities of the world and how they are developing.
As a side opinion....with the exception of London, this documentary sure made me feel thankful that i do not live in ANY of these "mega cities"..as it shows life in them to be just plain awful.