I was in the Seaport last week and walked past this site on all 4 sides. With some meat going on the bones it is obvious that this is one of the most aesthetically transformational developments in the area.
Firstly, it adds vast stretches of streetwall to Seaport Blvd and Northern Ave. That is really going to enclose Seaport Blvd and make it feel less vast. Northern doesn't really have the same scale problem, but the enclosure will be welcome there nonetheless.
Second, it hides Vertex and 1MPD from most vantage points. It won't be the prettiest building in Boston and probably not even in the Seaport, but for it's massive landscraper proportions it manages to avoid being as monolithic and cold as its neighbors. Vertex and 1MPD will finally melt into the background as they were clearly meant to.
It won't be too long before this phase of Seaport development is a distant memory (of a nightmare).