I go to Mumbai twice a year for work, usually in April and then November. I stay near the airport (Courtyard Marriott) as it is easy for meetings etc.
It is a wonderful, relentless, busy, dirty, exciting city. It looks much better at night than during the day. Traffic is a pain.
Some parts are the worst slums I have ever seen, and then less than 5 kms away, it can feel like you're walking down near the Riviera.
There are wonderful restaurants, but take all the usual precautions like in other parts of Asia. Luckily I've never been sick in Mumbai.
The local street food is called Vada Pav - deep fried spicy potato patty in a roll. It is fantastic. Everyone in Mumbai loves them.
Indian wine can be pretty good. Sula is what I usually drink when there (along with Kingfisher Ultra).
If you have time, get along to a cricket match. My favourite cricket stadium (after the SCG) is there. Amusing name too.
If you want to get out of the city for a couple of days, I would recommend Goa - but I haven't been there since the 1990's, so I imagine it has changed a bit since I was there.