Why not just wait with all the complaints until more information are provided and the Galaxy client is available? If it can fully replace the old GoG downloader, i.e. downloading and keeping the original installer but not automatically installing any games, then wouldn't it be fine? I imagine it will be very convenient to have the games library in the client instead of the web browser with some status information ("ready to download", "downloaded, ready to install", "installed and ready to start with one click", ...)
And as the GoG team said, it's fully optional. For directly downloading the bigger files from the website, any download manager will still do the job. They also have some kind of integrity check, haven't they?