Comment 2 for bug 281966

Because it needs to remove important packages:
The following packages will be REMOVED:
  human-theme ubuntu-artwork ubuntu-desktop
The following NEW packages will be installed:
  gtk2-engines-ubuntulooks

Either way, use aptitude ;)
$ sudo aptitude install xubuntu-desktop
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reading extended state information
Initializing package states... Done
Writing extended state information... Done
The following packages are BROKEN:
  human-theme
The following NEW packages will be installed:
  a2ps{a} abiword abiword-common{a} abiword-help{a}
  abiword-plugin-grammar{a} abiword-plugin-mathview{a} abiword-plugins
  aumix{a} catfish cupsys-driver-gutenprint exo-utils{a} gnumeric{a}
  gnumeric-common{a} gnumeric-gtk gpicview gtk2-engines-ubuntulooks
  gtk2-engines-xfce libaiksaurus-1.2-0c2a{a} libaiksaurus-1.2-data{a}
  libaiksaurusgtk-1.2-0c2a{a} libdiscid0{a} libexo-0.3-0{a} libgda3-3{a}
  libgda3-bin{a} libgda3-common{a} libgdl-1-0{a} libgdl-1-common{a}
  libgdome2-0{a} libgdome2-cpp-smart0c2a{a} libglib2.0-data
  libgoffice-0-6{a} libgoffice-0-6-common{a} libgoffice-gtk-0-6
  libgsf-gnome-1-114{a} libgtkmathview0c2a{a} liblink-grammar4{a}
  libloudmouth1-0{a} libots0{a} libt1-5{a} libtagc0{a} libthunar-vfs-1-2{a}
  libtunepimp5{a} libxfce4mcs-client3{a} libxfce4mcs-manager3{a}
  libxfce4util4{a} libxfcegui4-4{a} link-grammar-dictionaries-en{a} listen
  mousepad mozilla-thunderbird orage psutils{a} python-ctypes{a}
  python-gnome2-extras{a} python-musicbrainz2{a} python-ogg{a}
  python-pymad{a} python-pyogg{a} python-pyvorbis{a} python-tunepimp{a}
  slocate{a} tango-icon-theme tango-icon-theme-common thunar
  thunar-archive-plugin thunar-data{a} thunar-media-tags-plugin
  thunar-thumbnailers thunar-volman thunderbird{a} vim-runtime xchat
  xchat-common{a} xfce4-appfinder xfce4-battery-plugin xfce4-clipman-plugin
  xfce4-cpugraph-plugin xfce4-dict xfce4-fsguard-plugin
  xfce4-governor-plugin xfce4-icon-theme{a} xfce4-mailwatch-plugin
  xfce4-mcs-manager{a} xfce4-mcs-plugins{a} xfce4-mcs-plugins-extra
  xfce4-mixer xfce4-mixer-alsa{a} xfce4-mount-plugin xfce4-netload-plugin
  xfce4-notes-plugin xfce4-panel{a} xfce4-places-plugin
  xfce4-quicklauncher-plugin xfce4-screenshooter-plugin xfce4-session
  xfce4-smartbookmark-plugin xfce4-systemload-plugin xfce4-terminal
  xfce4-utils{a} xfce4-verve-plugin xfce4-weather-plugin xfce4-xkb-plugin
  xfdesktop4{a} xfdesktop4-data{a} xfprint4 xfwm4{a} xfwm4-themes{a}
  xubuntu-artwork-usplash xubuntu-default-settings xubuntu-desktop
  xubuntu-docs
0 packages upgraded, 111 newly installed, 0 to remove and 2 not upgraded.
Need to get 66.5MB of archives. After unpacking 269MB will be used.
The following packages have unmet dependencies:
  human-theme: Conflicts: gtk2-engines-ubuntulooks but 0.9.12-12 is to be installed.
The following actions will resolve these dependencies:

Remove the following packages:
human-theme
ubuntu-artwork
ubuntu-desktop

Score is 257

Accept this solution? [Y/n/q/?]