Impressed with IE11.
Finally loaded the Windows 8.1 preview on one of my desktop machines yesterday. Still getting used to the changes, but one thing that stood out immediately is IE11. Wow.
In addition, site compatibility is much better. As a proof point, I'm using the native post editor on theverge.com right now in IE11 without having to enable Compatibility View. I'm sure that standards support is improved, but I think the real reason for this is that Microsoft has eliminated the 'MSIE' tag from the browser's user agent string, "tricking" poorly implemented sites into treating IE11 as a standards-compliant browser.
It's a very nice update. Thanks Microsoft!