Apart from the great decor at the airport. The immigrations experience to enter Mumbai is terrible.60 odd counters available and only a fraction manner .more than an hr in queue is lousy.
Traffic congestion due to construction activity at and near the international airport will set you back 30 to 45 minutes so factor that into your schedule
Immigration are simply just rude, its a pity that they are the first Indian people you meet. Once you get past these guys, the real Indian people wait.
The airport lounge is still at temporary location. Not well equipped nor comfortable. Looks more like a gate waiting room. They should try to get rid of the mosquitos too.