One of my favorite hotels in SF, and I've stayed in many
I have stayed here several times over the past year, and with the exception of my first stay, the service has been extraordinary. The first time I stayed here a few months ago, the service of the front desk wasn't very welcoming, and I wasn't expecting construction at the hotel either which was a little inconvenient at first. I wasn't thanked for being a platinum member either, as I normally am at other Hyatts. However, that experience was short lived, because every stay after that has been a 180 degree turnaround from the first. The staff has since been super friendly after that first experience, always welcoming me back (I love when hotels recognize return guests) and even remembering my name, as well as my dog's name! Construction is still fairly inconvenient, but the quality of service, as well as the rooms make up for the inconvenience. 
The rooms are very nice, contemporary and very clean. I have always requested a high floor, and with availability, they have never had a problem honoring my request. The higher floors have AMAZING views. Each room has floor to ceiling windows with automatic blinds that you can operate while lying in bed. I'm also very particular about bathrooms at hotels, and I have nothing to complain about with these ones -- They are always spotless (I always look at corners, and dirt between tiles, etc.), and showers have a detachable head and plenty of counter space. 
The location is another plus with this hotel. It's located almost in the heart of Union Square, only a few blocks from Chinatown, in a crowded part of town, so to be able to walk out of the hotel and down the street to shop, eat, or sightsee without having to deal with taxis, parking or public transportation is awesome. I have to say that the only drawback would be the noise from the downtown streets late at night. Although the windows seem to block out most noise, I could still faintly hear echos of crowds of people, concerts, trucks, etc. even from the higher floors. But the noise from outside has only been a minor thing.
This hotel is one of my favorites to stay at in San Francisco, and I have stayed in many. A colleague noticed me say a few times: "I'm going home" instead of "I'm going back to my hotel" which shows the kind of sentiment I feel being there.