And as expected, it's getting ripped in the comments. Having visited it, count me generally as a fan. I give it an A-. Once the trees fill in and mature, I think it might become pretty great. I don't know what people are expecting. Copley Square never was/is/will be a "park" with a large, lush green lawn. All the commenters are expecting it to be a park. When was it ever a park in that sense? Great cities have bricked plazas all the time; who is to say that every public space should be a lawn? The point is that it should be a piazza, and can be some day if they close the street, but in the meantime, this new configuration will serve the city better than the mud patch that was there for years.
I dont see anyone on here saying it's that they bricked over the lawn. It's that the design they used produced a finished product that is overly exposed and visually and aesthetically hostile, cold, and hard. Ditto the materials: as many have said here, the color and the material and the material patterns itself matter enormously for spaces like this, and make or break whether someone feels warm and invited into the space versus alienated and driven away. This is like the most basic design stuff, nothing magical or overly demanding here. And another thing that is very basic is to take into account the surroundings. This space is surrounded by warm grays and terracottas on three sides by architecturally significant buildings, with large, monumental structures. A good designer would have taken those tones into account, and would have also used either much smaller, or much larger paving stones. The small, slender, alternating shades of gray slabs look like kitchen tiles and they would not look so anywhere, but they do when Trinity Church or the BPL is in the background of one's vision.
If you're deviate from basic design principles such as "let's heed the local context here", you gotta really know what you're doing; otherwise, it just looks like you as the designer didn't give a shit or bother actually even visiting the space you drew up to build. Obviously there are differences of taste, but really, I think most designers of urban space would agree that Copley could have been done a lot better and the ways in which it fails are quite obvious, and for a space with this much significance, the city royally blew it. Because Copley, as a centerpiece urban space for this city, deserved better.
Editing since I realize you're referring to the Globe article comments not (perhaps) the comments here on aB. But I suspect that without consciously being aware of the various design flaws here, people are saying they hate the hardscape when they really just feel the aesthetics that make it exude a hardscape feeling. Just like good design can make small spaces feel big, cold spaces feel warm, etc etc...