I have traveled with Indigo many times through out India. As per my suggestion is the best domestic flight operator inside India. Most of the time flights are in time and the behavior of staff is good. The best part of the flight is the leg space they provide which is much better as compared to the other competitors. Prices of the flight tickets are also within the range especially when you are travelling between two big cities. Travel to the small cities are costlier but still they have better in network so that you can plan your travel to your home city or nearby airport to your home city.
The only concern is about their cancellation charges which is 2200 plus tax. By any chance if you are cancelling the ticket it cost a huge amount of money and that Indigo is not at all looking into. They need to make the cancellation policy or reschedule policy flexible to the customer. One more concerned I found is that do not provide PDF file or an attachment for the travel itinerary.
Many of the travel website does provide ticket of Indigo and make it as a ticket without check in bag hiddenly. So be carefull while booking ticket via third party website and app.