What impact did monetary policy actions taken during the Great Recession (2007-09) have on U.S. economic performance? What impact did monetary policy actions taken during the Great Recession (2007-09) have on U.S. economic performance?

Quantitative easing and unconventional policy actions such as asset purchases and "forward guidance". I think I'm missing some things.
The consensus appears to be that the effect was large and positive. The IGM Forum asked a panel of economists to assess the statement

"Informed postmortems of Ben Bernanke’s Fed chairmanship will judge favorably the Fed's creative and aggressive policy initiatives from autumn 2008 through early 2009."

Not one disagreed. Weighted by their confidence, 90% of those polled agreed or strongly agreed with the statement.

http://www.igmchicago.org/igm-economic-experts-panel/poll-results?SurveyID=SV_1GF6NyHSVWhEtN3