The election does not appear to have been "irregular" in the sense of rigged ballots. It does, however, reflect a continuing pattern of national interest groups and money flooding state and local races. The tactic has now been used to defeat gay marriage in several states, and to elect Republicans like Brown.
When the election is in just 1 state or Congressional district, but the campaign effort is waged with outside resources & workers from all 50 states, then a distortion of the parochial interests of the local resident voters becomes a danger.
Of course, this has always happened to some extent before, but never on this scale of money, resources and coordination.