Ironically, the densest city in New England is something of a desert for good transit. No trains except Davis, and the Orange Line running just along the other side (but with no stations *in* Somerville until Assembly opened.) Of the 14 "high value"[1] bus lines, none touch Somerville, while 5 run in Cambridge.

[1] I don't know the T's definition, but it's the same as my list of buses that ostensibly run at least every 20 minutes at all times, not counting post-midnight. That was lowering my standards from 10 minutes, but hey, "world class city" cough cough.