In order to answer these questions, we need to compare this year to others.
The following charts show first the change in Offensive/Defensive efficiency for each team in the 2010-11 and 2011-12 Premier League, and secondly the change over the last three years (when shots/shots faced statistics became more readily available). In the first graph, lines chart the year-on-year change for each club. Such lines aren't present in the second chart as they would make the chart practically unintelligible. Enjoy!
I highly recommend clicking each image to enlarge it.