If Total number of medals (Gold + Silver + Bronze) won at Olympics is a parameter for measuring the success, then 2012 was India’s Best Olympics Ever! See:
Data Source: http://en.wikipedia.org/wiki/India_at_the_Olympics
Note: I filtered the Games that India did not Participate in. Those years are: 1896, 1904, 1908, 1912.
What do you think?