To put it simply, Mumbai is a crowded metropolis, and like many large cities there is large economic variability. I think of the Chicago that I am familiar with, from the South Side to the Gold Coast, and the differences in population of these two areas. However, I think the size of Mumbai and the growing economic prosperity of the 'upper' and 'middle' classes here provide a stark contrast to the hard reality of poverty that millions in Mumbai live in.
Previously, there was a smaller subset of Mumbai that lived in the money, mainly the Bollywood elite and business moguls. Now with the burgeoning middle class that has more disposable income the look of Mumbai is changing. Nowhere is this more evident than my in-laws own little neighborhood. Mumbai is divided into neighborhoods similar to the way Chicago is, but then these neighborhoods are divided even further.
My in-laws live in Ghatkopar West, a run of the mill area of Mumbai; nothing special or outstanding about Ghatkopar until a few years ago. You walk out of their building and you have roadside stall selling everything from vegetables to underwear. There are also several small stores selling everything from milk and dry goods to jewelry along with some store front doctors offices. The beginning of 2009 brought big change to Ghatkopar and really put it on the Mumbai map, R City Mall opened up. R City is now the biggest mall in India with four floors of stores including a large food court (KFC, Subway, Dominos, and more), a 9 screen movie theater, an indoor 'ice rink' (actually some sort of tile that you can skate on), and an arcade that has a 6 lane bowling alley. This is a mere 5 minute rickshaw ride from my in-laws.
However, just outside kids are begging, people are living in shanty houses, and others live in a pile of garbage and 'pick' what they can use or resell.
Like I said, a city of contrasts.