I don't use KDE these days but I think that in the past Kplayer used to come as a part of the Qt/KDE desktop, so say that you've Kubuntu, then most probably you don't need to install it manually.
However apart from all those features and a beautiful GUI, if you use Ubuntu, then while installing Kplayer will take some space of your HDD since it's a part of the KDE project thus needs to download a lot of dependencies which in my case, apt-get told me that she had to download about 72MB + files in size!.
|Kplayer in KDE 4x desktop...|
*. Lots of features (typical KDE, lol).
*. Playlist support.
*. Enable/Disable subtitles.
*. Direct play URL, DVD, VCD, audio CD, DVB, etc.
*. Change video contrast, saturation and hue.
*. Play/Pause/Stop/Next... you know the typical toolbar (which is also customizable thus you can enable/disable + create a tool-bar of your own).
*. Multimedia library support (handy if you have a big collection to manage).
*. Output messages that let you see the playback output and advanced codec information, etc.
*. Audio and especially video filters (de-interlace, post-processing, etc).
These are just a small list of its main features to mention. As you can see, Kplayer easily beats the Totem (the Gnome's media player) by a huge margin ;-). Anyhow, you can install Kplayer in Ubuntu 11.04 Natty Narwhal, 10.10 and 10.04 by using the below command in your Terminal window.
sudo apt-get install kplayerThat's it. Enjoy!.