That may sound trite, because it is. It's also true.
It's IE9 with IE10's substandard HTML, JS and CSS stuff shoehorned in. That doesn't even make for a better IE9, it makes for a completely different beast of a browser.
Realistically, I'm only ever going to use it to browser test, so for me and possibly everyone else here on HN, the most important feature is going to be the developer tools. And in this version of IE What's not to like?
Everything. That's what. All it's good for is checking the console, but even then it's like having your debugging info spoken to you by a special needs kid with a lisp. Objects are still just the ever useless [object Object]. Minor javascript errors are enough to send it into a tailspin, followed up by an inevitable crash. I still don't understand why the console displays line numbers as links when clicking them does nothing. Profiler and Network, yeah, they do their job ok-ish, but they do the bare minimum.
Also, I wonder: when they had the meeting at Microsoft to decide what to call the "disable cache" option, which bight spark suggested "Always refresh from server" would be the best label to properly convey the feature. Probably the same bright spark who decided to make it do absolutely nothing so you still have to empty the cache every fucking time anyway.
My rating: 0/10. As far as I can tell, there's not one single aspect of it that's in any way better than anything the competition offers. Zero "things" that could earn it even a solitary point.
I'm sick to the back teeth of IE and it's bullshit. Three sarcastic cheers for yet another turd we all have to work late to support.