First and foremost, there's a new networking stack - or, more accurately, lwIP has been ported to ReactOS. Both stability as well as performance has been improved this way, so that even things like torrents can download just fine now. Compatibility with NT 5.1 drivers has been improved, and it also supports wireless networks, both open and WEP.
Users can now also install and use XP-based themes to prettify their ReactOS experience - or simply revert to the classic theme, of course. In addition, thanks to the addition of a kernel mode testing framework, several issues regarding kernel mode components have been identified and fixed, improving core stability.
Another major change is this: "Support for building ReactOS using the Microsoft toolset has also played a large part in the release. This is now at a stage where ReactOS can be entirely built using an MSVC based environment and can produce a working boot and livecd. Along with GCC, ReactOS can now be built using two different toolsets and on a variety of platforms including Windows, Linux and Mac OS X."