Nice place for families
We decided to stay at the San Carlos after reading mostly favorable reviews on TripAdvisor. We had a 12th floor executive suite facing 50th avenue, from 13 to 19 September.
Hotel location is OK, many restaurants at walking distance, 2 blocks away from subway station, lots of groceries stores nearby, friendly reception staff. Housekeeping is efficient. Free internet access, I could use two devices simultaneously under the same login. No room service.
The suite is large is disposes of kitchenette with microwave and fridge, although a toaster would have come in handy. It is quite comfortable for two people, with plenty of drawers and storing space, sofa and a small dining table with two chairs. Beware of the touch-sensitive mini-bar, unless you really want to pick up something. There are 2 large flat screen TV sets, but the program grid is limited to US channels: no French, German or Italian channel, which could add an international flair to the property. The bathroom has magnifying mirror, towels of good standard, satisfactory but not high-end toiletries. 
Bed is comfortable, there is a good choice of pillows, but sleep quality was greatly disturbed by persistent air-borne noise. The windows are definitely not soundproof (the site call them "double-glazed"), and every kind of street noise seemed to pour into the room, from shouts and whistles late at night, to police and fire sirens all night long and delivery trucks early in the morning.
Breakfast was better than I had expected from previous reviews. It is the usual continental type, and one would not pay less than 13 euros for it in a Parisian hotel; we would complement it upstairs with some fresh fruit bought the evening before. The breakfast room is really cramped, although that is a minor problem if you are on vacation and can manage your time schedule avoiding breakfast at peak times.
The San Carlos is a nice and affordable hotel in NY, adequate for a short stay and particularly suited for families with children.