It is an evolution of the previous version. It's focused mostly on introducing New features, several of them to bring back parts of the old FCKeditor feature set, but there are also new parts like the integration with jQuery and the new Paste system that allows to have a control about what's being pasted into the content.
As these features have been rewritten, don't be surprised if there's a little bug here and there, so if you're sure that something isn't working then head up to the dev site and search for existing bugs (if it's something obvious and easy to reproduce it's highly likely that someone has already reported it). If you can't find any ticket about the problem then file a new one with the steps to reproduce the problem (what's the browser, a sample page to load, what must be done after the page is loaded...) and then if it's confirmed it might be fixed in a future release.
Just remember that there's a lot of work going on in CKEditor as you can see in the roadmap.
The simple announcement by Wiktor explains it well, some little bugs, improved compatibility and new translations. The focus of the work is now on the new version that will try to address the missing features that are requested in the CKFinder forum and trying to look even further by making it possible to create more easily new features in the future that no one has dared to request.
There's one thing to notice about this release, as I explained in the previous post Firefox 3.6 hasn't included support of onreadystatechange and the previous versions of CKFinder fail to enable the upload button. The new release includes a little workaround so download CKFinder before your users upgrade to Firefox 3.6 and they call you to ask why does it fail.