These directions are partial modeled from this video by Ironclaw, so props to him.
Wine must be installed. Run winecfg, and in the Graphics tab, pick the Emulate a virtual desktop option with a resolution smaller than your screen for now.
pacman -S wine
winecfg
Get the Deus Ex GOTY edition (DRM free) from GoodOldGames.com or get it for free from a torrent (expect it to be labelled with GoodOldGames or GOG)
cd into the directory. If you have the GOG version, there should be a setup_deus_ex_2.0.0.11.exe file, or something of the sort. Run that in wine:
wine setup_deus_ex_2.0.0.11.exe
Either change your default install location to something more memorable (it will be in ~/.wine) or mark down the location they give you. My install location was ~.wine/drive_c/GOG\ Games/Deus\ Ex\ GOTY/ by default.
Now we can download and install the improved OpenGL renderer and put it into the Deus Ex System folder.
curl -O http://cwdohnal.com/utglr/dxglr21.zip
unzip dxglr21.zip
cp OpenGLDrv.dll ~/.wine/drive_c/GOG\ Games/Deus\ Ex\ GOTY/System/OpenGlDrv.dll
Remember that since Wine is emulating a Windows machine, it will get confused if two files exist in the same directory with names that differ only by capitalization, so be sure to overwrite the exact file that is present in your System folder. The lines above worked for me.
Now we can run Deus Ex with the command below. You can make an alias for this in your bashrc if you don't want to type it out all the time.
wine ~/.wine/drive_c/GOG\ Games/Deus\ Ex\ GOTY/System/DeusEx.exe
Sometimes it will crash on startup. Just kill the process and try again; don't sweat it.
We're not quite done yet. Run the command above and choose the option to manually select your 3D video device. Select the Show All Devices choice to reveal the OpenGL Support option. Select that and continue.
The game should start. If you don't have audio, try installing the packages below:
pacman -S lib32-libpulse
This worked flawlessly with the latest GOG release (It's $6); bought it on GOG because I have the Steam version but that seems more work. Was able to get it installed and running on Artix