The biggest addition is a new feed showing what your friends are playing, when they earn achievements and make forum posts. You're broadcasting your own activity by default, though that can be tweaked in settings. You can choose to have your profile, game library and friends list viewable by everyone, friends or just you, similar to Steam's recent privacy changes.
But even after setting all personal broadcasting to private, some activity and profile information is still shown, RPS noted. Whether increasing social visibility ends up being a good thing for GOG, users are making themselves heard on the platform's forum, from those welcoming the new changes to diehards resisting any change from the marketplace's previous social agnosticism.