I stayed here for 2 nights this past December and was very happy with the hotel location. It is very close to the Garden and a short distance from Quincy Market. The room was clean albeit fairly small. We were given the option to choose 3 upgrades - via an email several days before our stay - that we did not avail ourselves to. We could have had a larger room for $50 extra per night, early check-in or late check-out for a nominal fee. There is free coffee, hot chocolate and spa-water in the lobby all day long and a bar with some light meal options. The hotel is pet friendly but doesn't smell like it. The staff are super friendly and helpful with directions, recommendations, etc.
The negatives are that you have to pay a small fortune to valet your car here. The walls are also pretty thin and we had a romantic couple on side and an "excited/emotional" child on the other. The work out room is in the basement and is very small and sparse. I think there were 3 treadmills and 2 bikes. They had run out of towels and it didn't look like a lot of attention was being paid to it. Ice machines are located on every other floor.
I would stay here again but likely upgrade to a larger room.

Cute boutique hotel! Rooms are beautiful, functional and the beds as with all Kimpton hotels are the best! The hotel is in a great location, very close to the Garden and T if you’re looking for that. The customer service was excellent, used their “forgot it, we got it” service and had hairspray up to my room in no time and had the bellmen hold my luggage after check out so I could do some shopping as I was not leaving the city until later in the afternoon. The lobby area is small, they host their evening wine hour there and it can get a bit crowded with people coming and going.

The service at this hotel was amazing. I've traveled all ove the world, and have never run across such accommodating, cheerful helpful staff. Lauren and Michael at the front desk were especially kind. The rooms were fabulous - clean, spacious, beautifully decorated. The beds were the most comfortable of any I've ever slept in!! When we arrived, we were greeted by chilled bottled water, a plate of fresh sliced fruit, and a very nice handwritten note from the hotel staff. The buffet breakfast was superb. Every evening a free glass of wine was served in the lobby. Coffee/Tea service in the lobby in the morning was complimentary, and was of the utmost quality. There was always iced lemon water in the lobby also. Such attention to detail is not common nowadays. We had appointments at Mass General Hospital, and asked to leave our luggage in the room after checkout time. It was no problem. I can't say enough nice things about this hotel!! Roger, Karen and Lauren Quirk, Lubec, Maine.

Kimpton hotels are generally pretty awesome and I have to admit i was psyche to get to try a new one in Boston. The onyx is close to Boston garden in the north end, and since I usually stay at the Marlowe in Cambridge, I was excited to see how the onyx fared.

Let me say this - it was a solid hotel experience, but not as good as my other kimpton stays. The bed was fantastic, the furnishings and style top end, but I missed the designer public spaces and high quality restaurant/bar i've come to expect. This felt more like an efficiency hotel for someone who was not going to spend any time in the hotel. Plus: they had a car service ready to go on demand, which was a lifesaver as it was tricky to catch a cab. Minus: the lobby/restaurant was small and not as welcoming as other kimpton properties.