The mem going around the left these days is that the Democrats should have won Congress but didn't because the nasty Republicans cheated by gerrymandering the system. While it may be true that more people voted for Democrats for Congress than voted for Republicans, this does not prove anything. There are some more important factors at work. The most important one is that Democrats tend to live clustered together while Republicans spread out more. This has its own ramifications.
Ohio was the swing state this year. Given how closely balanced the Ohio electorate is you would expect it to have equal numbers of Democrats and republicans but if you look at a map showing concentrations of voters you find that President Obama's support came from a swath across the northern part of the state plus the areas around Columbus and Cincinnati. The rest of the state went for Romney.
If you draw simple Congressional districts then you only end up with three or four Democrats. The only way to get more is to chop up the cities and add them to more rural districts. But the more you do this the stranger the districts look. No matter how you chop it up, it is going to look like gerrymandering to a neutral observer. There is just no way around this.
This also ties into minority rights. Minorities tend to vote Democrat and the thinking for decades has been to create minority districts in order to assure the election of minorities to Congress. Any change to this system would be treated as a threat to minority representation.
Another factor caused by Democrats clustering together is that votes count more in some states than in others. To keep Congress from having over a thousand members, the smaller states get more representatives per citizen than the large states get. Most of the small states vote Republican and the large states vote Democrat.
There are some other factors at play. 30 states have Republican governors. Since you can't gerrymander a state, this implies that Congress should be 60% Republican. The fact that it isn't shows the importance of incumbency and wave elections. Many of those governors were elected in the wave election of 2010. The House of Representatives also changed hands that year. The new districts were drawn after an election where the Republicans won big.
Incumbency should never be ignored as a factor. We had three wave elections where multiple districts changed hands, two in which Democrats made gains and one in which Republicans reversed this trend. And these took place before the most recent redistricting. Part of this is because both parties fight hard for safe districts but part is also because in an ordinary election, people tend to vote for the person already in office. The system is set up to favor the incumbent from either party. While we did have a series of wave elections, this is unusual. The House has only changed hands three times in the last 50 years and two of them were in the last six.
A case can be made for making more districts competitive. Currently the most radical members of Congress, especially from the left, come from safe seats. Having more competitive districts would tend to favor more moderate candidates but the current complaints about gerrymandering have nothing to do with that. They are the coming from people who are offended by the very idea that the election was a status quo election.