Extremely convenient location/extremely comfortable room.
My husband and I had a great experience at the Copley Marriot and I'd recommend staying here to anyone visiting Boston. 
The location is so convenient - attached to the Prudential centre mall (which includes a grocery store if you want to pick up any food to save money on meals), right next to the T, steps from the Public Library, and about an 8 minute walk from boston common. 
Great experience in the hotel; it compares with 4-star accomodations like Doubeltree, etc. We checked in 3 hours early, no problem. The room was a decent size with semi-stylish furnishings (it must have been recently updated) and a nice view. The king sized bed was so comfortable. The room's AC was icy cold. The wifi in the lobby worked well. Surprisingly, the hotel's bar and restaurant were always packed. While we didn't eat here, it was nice to see that it had a cool scene and would have been a decent option for an easy night "in" while travelling.