There are really thee possible scenarios I see:

1. The GOP-controlled house (assuming they don’t get the senate) causes even more gridlock than the GOP-minority house did. The Tea Party electees fall in line, doing what the GOP leadership tells them. Very little actually happens, except endless grandstanding hearings on climate change attempting to prove scientists are really very bad people.

2. The GOP leadership attempts to get a lot of shit done, despite not having the Senate. They try to woo conservative Democrats in the senate to get bills actually passed— like further reductions to the capital gains rate. These may prompt Obama to veto; depending on how spineless the Democrats are, his veto may get overridden. The deficit balloons because the GOP will not be cutting any significant spending, but is likely to, if given rein to, lower taxes even further. Socially conservative stuff is unlikely to survive vetoes, but will be hanging on every bill that goes through.

3. The Tea Party electees turn out to be completely uncontrollable and routinely disrupt business as usual, providing interesting theater but complete meltdowns. This means either:

3a. The GOP leadership tries to get them the fuck under control, leading to spats between the Tea Party/Palin types and the establishment types. The establishment ones are the ones who know how DC works, so the Tea Party morons can’t actually get anything done, but it turns into an interacine squabble.

3b. The GOP leadership goes along with the Tea Party wave, social conservatism is the order of the day, and things go seriously to shit, with completely partisan House investigations, impeachment attempts, massively socially conservative bills passed, and loads of Obama officials forced to testify in front of congress on matters vast and sundry.

Given that Boehner is openly campaigning for the dude who fetishizes the Nazis, 3b is really not so unlikely.