In 2009-10, Obama and the Democrats spent their considerable supply of political capital on the Affordable Care Act. The ACA proved to be Rube Goldberg contraption that nobody understood, except for the requirement of buying insurance, which they hated. The Democrats made matters worse in 2010 by trying to run away from the ACA and running on a platform of "we're not Republicans", which proved to be a less than optimal strategy.
I agree that a faster improvement to the economy would have helped the Democrats immeasurably in 2010. A bigger stimulus, which economists such as Paul Krugman and Joseph Stiglitz were calling far, would probably have made a big difference. Another thing that would have helped a great deal is if there was a huge oil glut in Obama's first couple years and corresponding fall in gas prices. This happened with both Reagan and Clinton in their first terms and I'm certain played a large role in the economic booms during their presidencies. This is probably ASB though, as I see little that the American government can do that would effect oil prices in the short term.
I agree that the ACA combined with the slow recovery hurt the Democrats big time in 2010, but healthcare reform per se need not have hurt the Democrats. I believe that if the Democrats had initially pushed for Medicare for all and negotiate down from there, then healthcare reform would have turned out better. After all, the portion of the ACA that everyone hates-the insurance mandate-is a conservative innovation. Conservatives proposed this idea as a mean of controlling costs through private insurance and avoid a government insurance program. The Democrats failed to exploit this flip-flop on the GOP's part.
All that being said, the mid-term congressional elections almost go badly for the party in control of the presidency, so the Republicans were bound to gain seats in either 2010 or 2014, if not both. But while the Dems were likely to have their control of Congress reduced, they should not have lost control of the House so soon after regaining it in 2006.