Internet Explorer delivers better standards compliance, but note that the point of comparison is Internet Explorer 7, and not the competition. This means that while the competition is pushing out beta releases that fully support Acid3, Internet Explorer 8 is finally ready to support Acid2.
Since IE8 comes with a whole load of changes to the Trident rendering engine to support all those standards, IE8 comes with a compatibiltiy mode that web developers can activate using an html meta tag. If IE8 reads such a tag in website, it will render said website in IE7 style, so they don't break.
There are also new features like Accelerators, Slices, and visual search suggestions. Accelerators allow users to invoke online services from the right click menu on a selection. For instance, by selecting "Warmenhuizen, The Netherlands" and activating the maps accelerator, you'll find out where I live (just turn right before nowhere).
Web slices are similar to the feature in Safari where a user can make a snippet of any part of a website and have it continuously update itself. Web developers do have to specify slices in their web page, and the format for doing so has been donated to the community as public domain.
Obviously, Internet Explorer 8 also comes with a boatload of bug fixes and performance improvements, as well as stability fixes. You'll be able to download the new release starting 16:00 GMT.
Personally, I've never been a fan of IE7, and IE8 will not make me change my mind. The issue is not so much the whole standards thing (although that only enlarges the resentment), but the interface. I have this paranoid idea that the Internet Explorer UI team has a photo of me in their office, and Ballmer ordered them to design an interface that would annoy that guy as much as possible. I just don't get the interface. Everything is in the wrong place, doesn't do what you expect it to, it's an inconsistent mess graphically, and far too busy and screamy for my taste.
Still, that does not negate the fact that improvements are being made in standards compliance, and that can only be seen as a good thing.