Quite a few had bigger casualty lists, and many were more specifically aimed at political targets rather than large numbers of public, but fair point that a bunch were very similar or worse-done.
Two points I would make about the comparison though, firstly the IRA campaign was very much one of fear more than one of death - deaths were an added bonus. Of course maybe that's the case in Boston as well, but it's too early to know right now. Secondly, the word used was "professional" - were the IRA professional? I guess in the context of terrorist attacks, that's probably not really a relevant term.