Cambridge is statistically dense overall because it doesn't have vast parklands or industrial areas like a lot of other cities do. Same for Somerville. That's not really the kind of density I was talking about (my criticism was based on aesthetic and highly localized planning considerations), but I would say these plots could use higher population density too. If nothing else it's a waste to have detached houses occupying land near a heavy rail station on a street that's contextually already a built-up commercial strip when there's such a high demand:supply ratio for space in the urban parts of metro Boston.
As for City Hall and MIT - civic and institutional buildings can and should be set off from the street. But more to the point, City Hall's lawn is, additionally, a nice public space, which these lawns are not. And most of MIT's open space isn't damaging the streetwall on Mass Ave.