Overall: a good experience
Meeting friends in Boston and where to stay? After a lot of research I settled on The Onyx partly because of the reasonable prices and partly because our friends had a good previous experience of the Kimpton brand. The welcome we had was excellent but the room was disappointingly small with a lot of rather large furniture in it. We had stayed in bigger rooms in New York hotels and that is saying something! There is efficient air conditioning in the room but it is very noisy, fortunately we did not need it on at night during our stay but we both agreed that during warm weather the noisy a/c would be very intrusive. The bathroom was spotlessly clean but there was no shower or bath gel only bars of soap and large bottles of shampoo and conditioner that were bolted to the wall - reminiscent of a budget hotel rather than the four star establishment that The Onyx claims to be. A sign on the bathroom shelf said that they would supply any toiletries that we needed ("If we haven't got it we will go and get it") but when we wanted bubble bath to ease our aching limbs in a hot bath after a day spent exploring the city, we were told that they didn't have any but that there is a "7/11 on the corner".
That said the front desk staff were very helpful and an honorable mention must go to Kate who helped us to find somewhere to eat even printing out the menus for us to peruse and then made the bookings.
The Ruby Room bar area is a dark and dismal but again the staff were keen and willing to help. Breakfast is served here which at $16 for a full breakfast it is quite pricey but there was plenty of it with cereal, fruit, a good selection of pastries as well as bacon, sausage and egg etc. 
I would agree with previous reviews that the area around the hotel is a little desolate at weekends and it is not quite as well situated as the Nine Zero which is the other Kimpton hotel in Boston which is reflected in the room rate. However everything we wanted to see and do was within easy walking distance and if you don't fancy walking there is a subway station just two blocks away.
Overall we had a very favourable experience and will consider staying at Kimpton hotels again when travelling in the USA in future.