Enjoyed our stay with only small complaints
First, I must reveal that we were in NYC for a wedding and our hosts had arranged for a group rate that was just over $200 per night, after taxes. In case you're not sure, this is an outstanding rate for NYC. This may have given us a bit more tolerance of minor shortcomings.
Our room was small, but engineered to be small and consequently was not oppressive. It was relatively quiet for such an enormous hotel; I don't remember being disturbed by sound. There are plenty of elevators, essentially no waiting (not true everywhere in New York, believe me). The lobby is large and yet strangely welcoming and comfortable. The staff is quite helpful and friendly.
We were there the first week in August, and temperatures were in the high eighties or low nineties (it was above 100 at home). Our room's air-conditioning just barely met our needs; in fact, my wife found it slightly inadequate. The thermostat claimed that we were getting colder air than we actually were. We did not complain to management, so I don't really know whether that could have been "fixed." I will say that this is not the first hotel in the city where we have experienced a similar problem; I think it's a building issue not a room issue—an attempt to control costs. As I intimated earlier, if we'd had a more expensive cost, I would probably have complained.
The bathroom was the size of one you might find on a small boat. Workable, but cramped. If a roomy bathroom is important, you might want to investigate further.
The biggest plus for this hotel is the location. The access to Grand Central is really helpful for transportation and (relatively) cheap food—not to mention how cool the station is.