At the end of 15 hours of “Ring” performances at the Canadian Opera Company last week, Robert Everett-Green surprised himself – hed’ do a repeat this week. “It helped that the COC’s production turned out to be good — better, in some ways, than the ones in those more famous opera houses I mentioned. There was a lot to admire and very little to cringe at, and the cringe factor is a large issue when you’re dealing with a work that offers so many insanely difficult problems in performance and staging.”