Arrival into Mumbai was fine went through to baggage claim fairly easy. However leaving is another matter. Very long lines at immigration took over 90 minutes from the beginning of the queue to the chap on the desk. Security after that is a nightmare taking forever to go through. After that there is not much in the way of duty free shops and the ones that are there are very expensive. There are a few bars which are not overly expensive but they give good service and are a happy retreat from the crowds. Overall not the worst airport in the world but very crowded to immigration so this needs to be factored into your flight departure.