Unless the Republican leadership gives up the "party of 'No'" label and starts compromising, it is highly unlikely that we will see any new major legislative bills like an Obamacare or a Dodd-Frank even come up for discussion (at least in the next two years).
Nevertheless, President Obama is not powerless. His reelection is still meaningful, as it will allow him to make sure that Dodd-Frank and Obamacare are both implemented to his satisfaction. Believe it or not, much of Dodd-Frank has yet to go into force two-and-a-half years after becoming law. The Securities and Exchange Commission (SEC) and the Commodities Futures Trading Commission (CFTC) have slowed the critical rule-making process down to give Wall Street adequate time to comment and prepare for implementation. In the meantime, they have both been fighting lawsuits filed by conservative groups that are bent on watering down the bill. If Romney had won the presidency, he would have certainly replaced the heads of both agencies with conservatives whose only mission would have been to slowly vote down critical parts of the bill. And there are plenty of critical parts still up for implementation, most notably, those rules governing derivatives.