Features the End, which is where you basically go to be killed by Ender Dragons ( not in this release yet ) and Endermen. They make use of the portals which are in strongholds which are activated by placing 12 ender eyes in the slots, once you go into the End however, there is no way back but dying.
Here is the download link first of all: http://www.minecraftforum.net/news/268-19-pre-release-4-is-out/
Enjoy,
-Karl