As expected, the release candidate includes much improved tab functionality, from the new square-ish visual elements, and moveable tab bar elements to increase customization. It also includes features that enable a user to refuse tracking from advertisers.
It also promises to fix a number of remaining bugs and minor annoyances that plagued the Beta and developer previews of the browser. The newer, more stable version of the browser needs to be pretty picture perfect if MS wants to regain its market share lost to Chrome and Firefox since IE8 started faltering.
We covered a preview of the new features here.