The filty rich, people dressed in filty clothes, and "people in between" co-exist in India. The first experience of India starts right where the airport ends - the crowd of touts and cabs fighting for your attention will come as quite a shock if you haven't faced it already.
The divide between rich and poor will become more profound once you leave the airport and enter the city. One second you are in a neighourhood rivaling the most plush cities in the world, another you are standing by a heap of garbage, watching children in rags hunting the trash for recyclable objects which they sell to earn their living.
India, specially the big cities, are complete chaos, owing to their large population. Someone from a quite neighourhood will be a bit taken aback when he is subjected to insane amounts of traffic accompanied with honking. For the most roads, you will have to jaywalk. However, don't concern yourself too much, as this is standard practice and drivers are used to it.
Apart from the traffic, cows and other animals roaming the strets isn't uncommon. They are big, but mostly harmless.
As far as society goes, the Indian society takes pride in being closely knit and valuing familial values. You will find people living with their parents, which is very uncommon in the west. Also, people don't display intimacy in public - even married people generally keep distance. On the other hand, boys with hands over other boys' shoulders, and girls holding each others' hands is a common sight.
Also note that the Indian states differ in culture at the macro level, and the country loves to fragment itself at both macro and micro levels. People from the northern part of India(believed to be Arayn descendents) and people from southern India(believed to be Dravidian descendents) are an example of culture difference at a macro level, and Tamil(South Indian) brahmins differentiating themselves from Non-brahmins is an example at a micro level.
India, as a country, has a different sense of privacy and personal space. People will ask all sorts of personal questions, without meaning any offence. It's just the Indian version of small talk, and they feel delighted if the same questions are asked of them.
Talk about programmers - you will find the bell curve at work. But since the number of people who are supposedly programmers is large, and you mostly come across the middle of the normal distribution, it's easy to get the impression that most people are incompetent.