Tested on CXG Mac 10.1.2, the actual game downloads fine on Steam but upon first-time launch, installation setup for .NET Framework 3.5 SP1 starts automatically and always ends in an installation failure (doesn't work on CXG at this time).
After exiting the .NET Framework setup, usually nothing happens although there was once the Punkbuster installation setup launches but also ends in an installation failure (doesn't work on CXG as well). Trying to launch the game again just starts the setup installations all over.
I'm not sure how to bypass the first-time setup installations, I've tried removing the setup executables for the .NET Framework 3.5 SP1 and Punkbuster from the game files which does stop the setup installations from starting automatically although nothing happens after that.
I've also tried directly running ROGame.exe under the game directory with CXG which also does absolutely nothing.
It's probably futile trying to run the game without .NET Framework 3.5 SP1 and Punkbuster anyway, so until those work, Red Orchestra 2 won't be able to run.