Lovely, upscale property
We drove in to the city. Even with a GPS, we drove by the hotel twice. It's not well marked. We finally called the front desk and asked for help. (FTR, if you are on Tremont, turn left onto the side street just before the Beantown Pub.) 
Nine Zero's location is outstanding if you want to do Freedom Trail activities. It is a few blocks away from Boston Common, which was great because we met our Tour Guide there the next morning. There are restaurants, drug stores, shops, etc, all within walking distance. There are also tons of historical sites right in the area, as well as a short walk away. We loved the Boston Common area. 
Most of the time, the hotel staff went overboard to make us feel welcome. However, one notable time, we sat in the chairs in front of the concierge table for five minutes before anyone bothered to ask us if we needed anything. 
The feel of the hotel is formal, despite attempts to lighten up the mood with whimsical touches, such as animal prints and zebra robes. Perhaps it's the heavy drapery they use on the walls, or the historic feel of the building, but we felt under-dressed walking through the lobby in our shorts and t-shirts. 
The clientele at Nine Zero is an eclectic mix. For instance, the complimentary wine reception was attended by a large family, including young kids, business people, young hipsters, and couples. Not sure who their target audience is, but I'd not return unless it was just adults. Oddly enough, their atmosphere is more welcoming of dogs than kids.
The rooms were small, but they fit a lot in, including 2 queen beds, a flat screen t.v., and work desk. As a family traveling, we appreciated the queen beds because the kids were as comfortable as we were. We also appreciated the robes, which made sharing one bathroom easier.
The concierge recommended a restaurant called Scollay Square. We wouldn't recommend it. Rather, we'd recommend a hole-in-the-wall restaurant called Artu, which our tour guide recommended. It's a short walk from the hotel.