I consider myself a very amateur architectural critic, but to me, I've very fond of this building. To me it says, Boston is still relavent and still in touch with trends. It's not so much that boston needs to be a "trendy" city, but when a current architectural style is noticebly missing, it is an indication that the city lapsed during a period.
As a popular trend now across much of the western world is minimalist, translucent, rectangles, I think this building scores very well against its peers. It takes a style that is difficult to engage at the street level, and does that well, while also providing subtle detailing, that makes it slightly more than a translucent recantangle, while escaping the now worn-out trend of visible x-bracing.
The fact that it is a "missing tooth" in my opinion is what makes it unique and invites further discovery by the average pedestrian. In this example, I think it excels, because the scale and detailing are correct, and the person who just did a double-take, will move on realizing that a tooth wasn't missing (can't be said for the corner of Newbury and Dartmouth), but that a snapshot of Boston history has been modified (tastefully) to include a small nod to a changing world.
The challenge will be for this to blend timelessly, which its too soon to know. I would argue that Back Bay's previous attempt (the "glassstone" on Marlborough near Hereford) failed in this regard, but it was a matter of context where the prevailing style there was so focused, it never had a chance to become part of the streetscape.
Ok...ending my faux-architectural critique....in other business, the crappy condition of theprint shop next door is now magnified next to this gleaming building.