How to download GOG games from the command line on Linux

If you are a gamer and a Linux user, you probably were delighted when GOG announced a few months ago that it will start proposing games for your favorite OS. If you have never heard of GOG before, I encourage you to check out their catalog of ???good old games???, reasonably priced, DRM-free, and packed with goodies. However, if the Windows client for GOG existed for quite some time now, an official Linux version is nowhere to be seen.