With appropriate codecs, DVD movies can be played in gxine, Totem movie player, VLC and kaffeine (for Kubuntu). I personally prefer the VLC player as it simply works, without having to do much configuration.
First, install the following library:
sudo apt-get install ubuntu-restricted-extras
This will install most of the codecs for multimedia (audio and video) playing.
The library package is not available in the Ubuntu repository, you have to use the libdvdread4 installer script.
sudo /usr/share/doc/libdvdread4/install-css.sh
This will retrieve and install the libdvdcss2. If it don’t work, download the deb installer at http://download.videolan.org/pub/libdvdcss/1.2.9/deb/libdvdcss2_1.2.9-1_i386.deb and click to install it.
Install the xine library
sudo apt-get install libxine1-ffmpeg
Install VLC
sudo apt-get install vlc
Now you should be to watch DVD in your VLC player.
If you want to use Totem Mplayer, you have to install totem-xine rather than using the default totem-gstreamer.
sudo apt-get install totem-xine