I've been away from professional web-dev for a while (kids!). My only real experience of IE10 is that I just handled an "IE10 on Win8 only" bug on a friends site so tested with IE10 and IE11 in a virtualised environment. I only have XP installs left of MS Windows.
Of course now that IE is supposed to work they won't let you use the conditional comment targeting method so I must - it seems - break it for IE11 by instructing all IE above 9 to fallback to IE9 compatibility mode.
Nothing else seems to fail with it and applying the hack (IE9 compat mode in a meta-tag) is problematic too.
Has IE changed that much?
That said the site is an application generated mess, it's painful. So maybe IE have really come around.
Modern IE is nice to use and has reasonable support. It will cost you as much (in dev time) to support as any other browser (or specifically, rendering engine), and its market share is comparable to Firefox.
The problem is old IE. fuck old IE and every bit of its ridiculous, antiquated and outdated self.
