FFmpegSource2 is the new default audio and video provider, replacing Avisynth. This should provide frame-exact seeking (with keyframe support) on AVI, MKV and MP4 files, as well as other benefits. This is still a bit experimental, however. If you have any issues, just switch back to Avisynth in options.
The DirectSound audio player was reverted to what it was in 2.1.1, since 2.1.2 seems to have critical issues related to it.[Edit: jfs says that the issue was after 2.1.2]
Many small issues around the program were fixed.
VSFilter has been updated to the MPC-HC 2.39 version, which includes jfs’s new patches (see this post)
Aegisub is now built against Visual C++ 2008 SP1 runtimes. Hopefully there will be no issues related to this (ASSDraw is still built against 2005 SP1 runtimes, due to library issues). If you can’t run Aegisub, try installing this and reporting how it goes.