I had a very nice experience here late last week. I want to briefly address the previous poster's comments:

-- Climate control was fine in my room.
-- GC rooms are on the 1st and 2nd floor of this hotel and I heard nothing from outside... I was on an inside-facing courtyard room, so perhaps that made the difference. There is absolutely no issue with flight noise in my experience.
-- The hotel is definitely a bit sleek and modern for my taste but jail-like is a little strong. The waterfall in the courtyard is nice indeed.
-- Standard-issue Hyatt international beds. Very comfortable for my taste.
-- I was there on the Friday of independence day weekend and yes, it was a bit empty.

The Grand Club is a particularly nice space and the gym is good, though I didn't try the pools. The restaurants are all fantastic, and this in a city filled with good restos.

The JW Marriott has an exquisite location on the beach and is a beautiful property. That said, I've found the staff to be among the worst in Mumbai. I am of Indian origin and I find that *some* Indian five-stars treat us worse than those who are obviously Western. I found none of this differentiation at the Grand Hyatt.

The downside is potentially the location depending on where you're working:Santa Cruz/Kalina is convenient to the domestic airport and to the growing Bandra-Kurla complex, but not to South Bombay, so think about this when you choose this hotel. For real South Bombay work, the Taj or Oberoi or the new Sheraton in Lower Parel might be better options. That said, I had no trouble finding taxi or auto rickshaw drivers who knew the Hyatt. Just make sure you tell them to go to the "Hyaath" hotel near the Western Express Highway in Kalina.

All in all, they've done a nice job with this property and seemed to get over the initial service snags. It's a major cut above the Hyatt Regency property in my opinion.

Just one final anecdote. Kalina was one of the worst affected areas in the recent floods with water levels supposedly well over 10 feet in parts. The GM of the Hyatt apparently opened up the hotel-- ballrooms and banquet halls, etc-- to people from the streets who were stranded in the area and couldn't get home. Kudos to the hotel for being decent corporate citizens in a time of crisis.