The default desktop for the VNC Server is “TWM”, though most people are used to KDE or Gnome instead. Here is how to change it:

Edit ~/.vnc/xstartup
For KDE, replace “twm &” with “startkde &”
For Gnome, replace “twm &” with “exec gnome-session &”
Kill any existing VNC servers with “vncserver -kill xx” where xxx is the display number.
Start a new server.