I do not think there is an important media player that is already in the latest SOHO, that is, mplayer.
mplayer is included with SOHO 5.1.1 but it is missing a menu entry. You can launch it with ¨gmplayer" or create a menu item using K Menu, Settings, Menu Editor.
On my current SOHO5.1.1, there is a mplayer plug-in that does not seem to work when I want to watch on-line video. It would be nice to be able to automatically download a missing plug-in or codec and watch a video right after, like in Windows.
mplayerplugin works fine for me. If you find it does not work with a specific media, please find out what media and tell us what codec you need. I think we have most codecs available from gslapt and our repository. We cannot help you unless you are more specific.
I think the Thunderbird email program is nice and you don't even have to install it, to get it to work. More software should be like that
I don´t understand what you mean. If a software package is pre-installed with the distro no, you don´t have to do anything (obviously). If you mean the binary install method you still have to download the program, navigate to the directory where you downloaded it, then run the installer. With gslapt all you have to do is click the program you want and click execute. So please explain what you mean.