Overall, there was similar improvement across the board when comparing 2012 to 2016. Congressional Democrats improved by 2.2 points, while senate Democrats improved by 2.8 points, and assembly Democrats by 1.7 points. That's a good showing but Hillary Clinton improved on Barack Obama's two party performance by 4.2 points. (Note: Clinton's two party percentage was 66.1% compared to Obama's 61.9%. The margin improved by double 4.2, 8.4 points) So Democrats didn't do as well as they could have. Democrats did have some districts with big gains, e.g. CA-49, 2, and 53, but not enough in any Republican held district to take it. There were a few places where the Republican congressional candidate did better than 2012, but there doesn't seem to be much commonality to the districts.
Some people don't feel Republicans did that well in 2014 because the party lost a congressional district. The chart shows the difference between 2014 and 2016 was dramatic. The average Democrat did 5.6 points better. The average margin in the 37 districts where a Republican ran against a Democrat each time increased from Democrats by 6.6 to Democrats by 17.8. Yet, these two very different results ended with the two parties winning the same districts each time. This wasn't due to gerrymandering creating safe seats. California lines are drawn by an independent commission. In 2014, won 7 districts by 5.4 points or less. That won most of them by much greater margins in 2016. Had Republicans just done a little better in 2014 and taken those districts they probably would've lost almost all of them in 2016.
Democrats picked up three assembly seats in 2016, but two of those AD-65 and 66 were ones they won in 2012, but lost in 2014. In fact, the Democrat did worse in 2016 in AD-66 than he did in 2012.