Almost perfect!
The staff at the hotel were all wonderful. They anticipated our needs, upgraded us from a Fenway room to a small suite at check-in, and gave recommendations when asked. The suite was very comfortable and the bedding was really plush. Eastern Standard had great dinner and breakfast, Island Creek Oyster Bar was bustling and fun, but we passed on eating there (good sign that the wait staff from Eastern Standard was there on their day off), and The Hawthorne had a really cool vibe. Additionally there are a few small stores in the hotel as well.
The ONLY things that kept if from being absolute perfection: 
1. The shower in the suite. It was a regular step-in bathtub with a bath mat that could have been purchased at Bed, Bath, and Beyond to lay down, a regular shower curtain and a stationary faucet that sprayed pretty hard. The rest of the bathroom was very spa-like and I expected the shower to follow suit-not to remind me of my bathroom at home.
2. I requested an in-room Keurig (I had LOVED that during a stay at a Fairmont) and received one, but would have preferred it be there without having to request.
3. Most of my concierge calls greeted me by name, however, it was not 100%.
I realize these are very small items and I truly recommend the hotel, but I am mentioning these items as my booking choice came down to here and The Fairmont and I chose Commonwealth based on the #1 spot on TripAdvisor. These things are not ones I had experienced at a Fairmont stay.