When all is said and done, it will be interesting to see what the long term impacts of the new towers on Boston.
My guess is that this tower's main legacy will be for what it does at street level/neighborhood revitalization in DTX. Architecturally, I'm guessing it will be a better than average, but non-iconic tower. It will be a peak on the DT skyline, but not tall enough to really dominate the already crowded skyline.
The Four Seasons tower will probably be the opposite. A transformative skyline tower that will have a visible impact on the city's skyline. But, given its tucked away location, I don't know that it will have much street level impact.
Copley seems like it will be somewhere in between. It has a far more prominent location (at street level than FS) looming over Copley Square (in a good way). Although, not as many will interact with it at street level as Millennium Tower, it will be a very noticeable addition to the built environment and might actually stick out more to pedestrians given the less structurally dense environment than DTX. It also might have more impact on the skyline than Millennium. Again not because it is taller or necessary architecturally superior, but just given it's prominent location on the less crowded Back Bay skyline.
At least 1 of Garden tower also seems likely to get started this cycle, but I don't have a good feel for it yet. Congress Garage and everything beyond that seems a little too hypothetical to really care much about at this point.
All and all, three great towers going up in this cycle that will each contribute to Boston in different ways, IMO.