In the weeks leading up to the election, the key question everyone focused on was whether or not the Republicans would get control of the Senate. It was never clear to me why that was supposed to be so important. As long as the Republicans control the House, the Democrats cannot pass any bills that the Republicans are solidly against. As long as the Democrats control the White House, Republicans cannot pass any bills that the Democrats are solidly against unless they have large enough majorities in both houses to override a presidential veto, which they were not going to get.
I do not want to overstate my case. A Republican majority in the Senate means that Obama cannot appoint judges, in particular Supreme Court judges, that the Republicans are solidly opposed to. It means that the Republicans can pass popular legislation that the Democrats oppose and force Obama to either sign it or veto it. It might make it possible to override a veto of popular legislation with the help of a few Democratic legislators. But the bottom line for legislation is still what it was. Nothing can get passed if either party is solidly opposed to it.
Which brings me back to my theory of why people vote. It isn't to change the political outcome, since any reasonable person knows that, in a large population polity, his vote has virtually no chance of doing that. It's for the same reason people go to football games—to cheer for their side.
In order to have a game you need some definition of winning and losing. In order for it to be interesting, the definition has to leave the outcome in doubt. If winning the midterm elections was defined by whether or not the Republicans retained their majority in the House or by whether they gained enough seats in both houses to override a presidential veto, it would have been a very boring contest, since the answer to both questions was known long in advance.
Viewing it as a contest over who ended up in control of the Senate, on the other hand, made it a game worth watching.