CrossOver Support - Community Forums

The GOG version will only show a grey screen and is unplayable.

It can be made to run by installing the unofficial patch from Knightmare, just copy the files over the GOG install.
http://www.markshan.com/knightmare/downloads/rtcw-sp-1.42d-win32-bin.zip

The game also looks much better with hi-res textures from
http://wolfenstein4ever.de/index.php/downloads/viewdownload/56-rtcw-sp-mods/2211-rtcw-hd-retexture-pack

You might want to check out https://github.com/iortcw/iortcw.git for a native build. From the readme:

The intent of this project is to provide a baseline RTCW which may be used
for further development and fun.
Some of the major features currently implemented are:

• SDL backend
• OpenAL sound API support (multiple speaker support and better sound
  quality)
• Full x86_64 support
• VoIP support, both in-game and external support through Mumble.
• MinGW compilation support on Windows and cross compilation support on Linux
• AVI video capture of demos
• Much improved console autocompletion
• Persistent console history
• Colorized terminal output
• Optional Ogg Vorbis support
• Much improved QVM tools
• Support for various esoteric operating systems
• cl_guid support
• HTTP/FTP download redirection (using cURL)
• Multiuser support on Windows systems (user specific game data
  is stored in "My Documents\RTCW")
• PNG support
• Many, many bug fixe