From 9 onward Microsoft took the web browser seriously, for probably the first time since IE 5 in, what, 2000? The problem was they had a decade of technology to catch up on and Trident simply had too much proprietary badness baked in to do a proper job of things.
But I'll argue that IE 10 and 11 were... not bad. Not great but not bad.
I *still* have to correct for IE11 bugs. It's maddening. And true-to-form, they recently snuck in an update with subtle changes that broke stuff which had been fine for months and months and months.
But I'll argue that IE 10 and 11 were... not bad. Not great but not bad.