Mostly depart\arrives on time. Clean cabin. On-flight food services are decent. Decent crew behaviour & ground staff. Affordable flight rates. Lot of flights to many destinations across India. 'Relatively' the best overall service.
Major area of improvement is ticket cancellation policies and associated fees. Will lose most of what you paid, if you decide to cancel tickets. Another poor practice is to pay for selecting seats.
------- Edited on 2016-12-06 -------
Have been a regular with Indigo for many years. It is my preferred mode of transport between Chennai >> TRV \ BOM \ DEL.
Pros : 1) Mostly fly on-time 2) Decent quality flights 3) Decent fares (not the cheapest) 4) Above Avg. Staff behaviour (mostly in-flight) 5) Mostly optimal routes (shortest time to destination. Some airliners show 24hrs to reach a destination while the actual flying time is <60mins!!)
Cons : 1) The seat selection option while booking on-line is a trap (just to add to the cost). Just book tickets and stand in a queue at the airport boarding pass counter to get conveniently allocated seats 2) Some ground staff and air-hostesses are a bit rude 3) Surge pricing 4) Expensive food on-board 5) On rare occasions have found unclean seats (esp. when I am boarding a connecting flight) 6) Poor support by Indigo for airport check-in kiosk (esp. @ Indiragandhi Int'l airport - DEL) 7) Not sure whether it is an Indigo issue, but maximum damage to my check-in baggage were with Indigo (esp. TRV) 8) Cramped seating (like most other economy class flights..some others are worse)
Few things to remember :
a. If you're a customer booking tickets on-line, just book tickets & take the print-out\email to the Indigo boarding pass issue counters. Do not need to pay extra at the time of booking on-line, just to get seats of your choice.
b. It is okay to carry light food while travelling domestic in Indigo flights. Please carry some snacks that buying on-flight.
c. Always buy good quality luggage covers for check-in luggage. Else your new poly-carbonate suit cases would start to look years old, in just few journeys
------- Edited on 2017-02-21 -------
The demand based pricing of late has been a poor model and ticket prices are 80% as expensive as Jet Airways, while latter manages to offer lot more for the money. Timeliness is mostly adhered. However, the staff behaviour is relatively less welcoming than what was it in the past.