One of the things that political scientists wind up doing when they comment on current events is telling people that the controversy of the moment isn't nearly as important as it seems. Midterm primary elections are the exact opposite case: these elections can be extraordinarily important events, and they're basically treated as afterthoughts by much of the press. It's a combination of things. The press generally undervalues the importance of Congress (while overvaluing the importance of the president). Moreover, they cover general elections more than they do primaries. Of course, general elections are quite important...but they're often not the actual, decisive, events. That is, by the time we get to November, the winners of all but a handful of House and Senate races will have already been determined, and for the rest the fact of uncertainty is often an effect of primaries. And there's a third factor -- the press usually focuses on either overall control of the chamber or net party gains and losses, but in the Senate single seats are quite important. Of course, that's a more difficult story to tell, but nevertheless it's true. Regardless of chamber control, it will matter who the 60th most liberal and 60th most conservative Senators are, as well as who will be the 50th/51st most liberal and conservative Senators. Beyond that, it individual actions of single Senators can simply make a big difference (remember when Richard Shelby held up all nominations? When Jim Bunning shut down debate even against the preferences of his party's leaders?).
It's also the case that while general elections are, to a large extent, consequences of relatively fixed factors (party identification, the state of the economy, the popularity of the president), primaries are often far more complex. They're intraparty contests, which often really are bitter fights over the leadership of a political party, in which party elites make choices and influence voter decisions. On the other hand, they're also low-information events in which money, campaign tactics and dynamics, and candidate skill may have large independent effects on voters. Of course, as underpolled and undercovered events, they're also full of surprises; Nate Silver says that final polls have been fairly poor predictors of election results during this primary season, missing by an average of about ten points.
All of this is to say that today's events, and in particular the contested Republican primaries in Delaware and New Hampshire, are really worth paying a lot of attention to. So: here's Ed Kilgore's backgrounder on the fascinating Delaware contest between moderate Mike Castle and flaky insurgent Christine O'Donnell, and here's Nate Silver's analysis of the effects of various results on November's results. See too Jonathan Chait's interesting comments on the GOP's choices and how some party leaders are handling them.
The two Senate races are clearly the headliners today, at least from a national perspective, but there's plenty of other contests to follow, including the Washington mayoral election and various primaries in Maryland and Massachusetts (all closing along with DE and NH at 8PM Eastern), and in New York, Rhode Island, and Wisconsin (closing at 9PM; as usual, Taegan Goddard supplies the poll-closing times). I also endorse the call from Matt Yglesias that obscure elections can be quite important, too. So, vote early, vote often, and good luck to all the candidates.