This guide walks through the steps necessary to install ut2004 ECE from gog.com using a SlackBuild that can be found at SlackBuilds.org.
mkdir -p /usr/share/games/ut2004/System
chgrp -R games /usr/share/games/ut2004
chmod -R 774 /usr/share/games/ut2004
exit
wine setup_ut2004_2.0.0.6.exe
wine regedit
a windows registry window will open up; navigate via mouse to find the CDKey located in HKEY_LOCAL_MACHINE/Software/Unreal Technology/Installed Apps/UT2004/
su root
vim /usr/share/games/ut2004/System/CDKey
cp -rfv ~/.wine/drive_c/GOG\ Games/Unreal\ Tournament\ 2004/* /usr/share/games/ut2004/
wget https://slackbuilds.org/slackbuilds/14.2/games/ut2004.tar.gz
tar -xvf ut2004.tar
cd ut2004
wget https://liflg.reto-schneider.ch/files/final/ut2004_3369-english.midway.dvd-3.run
./ut2004.SlackBuild
* Original source: https://www.linuxquestions.org/questions/blog/disturbed1-175451/native-ut2004-from-gog-com-3305/
* Originally written by khronosschoty