It varies by feature, but due to IE's long release cycle, it's generally about a year behind Firefox and Chrome on most things.
That's not entirely fair.
In terms of ticking boxes for new features, yes, IE certainly trails Firefox and Chrome by a few months, sometimes even a year or two.
On the other hand, when IE does claim to implement something, generally that implementation is fast, robust and stable. That certainly can't be said for Chrome or Firefox. Some obvious examples are the awful font rendering in Chrome (only just being fixed at the moment), lack of H.264 support for <video> elements in Firefox (still not fixed, just avoided on Windows with a workaround), and performance problems rendering SVGs that really undermine things like animations and using lots of SVG icons on a page in both browsers, just to pick three widely used recent features that all major browsers now claim to support.
While basic sites work, some things just aren't possible to do in IE yet.
That's very loaded terminology. Almost all real sites work just fine in any recent version of IE. The few that don't are mostly things like web design blogs and demos that push the bleeding edge because they want to.
Often these sites use features that aren't standardised yet and maybe still need browser prefixes to access the feature at all. These are exactly the kind of features that Chrome and Firefox tend to half-implement and then regress or change the spec several times over the next year or two before finally dropping the prefix. I doubt any professional web developer would actually use that kind of feature on a production site today unless they had very unusual requirements to meet. The example site you gave is another example of this.
That's not entirely fair.
In terms of ticking boxes for new features, yes, IE certainly trails Firefox and Chrome by a few months, sometimes even a year or two.
On the other hand, when IE does claim to implement something, generally that implementation is fast, robust and stable. That certainly can't be said for Chrome or Firefox. Some obvious examples are the awful font rendering in Chrome (only just being fixed at the moment), lack of H.264 support for <video> elements in Firefox (still not fixed, just avoided on Windows with a workaround), and performance problems rendering SVGs that really undermine things like animations and using lots of SVG icons on a page in both browsers, just to pick three widely used recent features that all major browsers now claim to support.
While basic sites work, some things just aren't possible to do in IE yet.
That's very loaded terminology. Almost all real sites work just fine in any recent version of IE. The few that don't are mostly things like web design blogs and demos that push the bleeding edge because they want to.
Often these sites use features that aren't standardised yet and maybe still need browser prefixes to access the feature at all. These are exactly the kind of features that Chrome and Firefox tend to half-implement and then regress or change the spec several times over the next year or two before finally dropping the prefix. I doubt any professional web developer would actually use that kind of feature on a production site today unless they had very unusual requirements to meet. The example site you gave is another example of this.