Braggadar: It's not across the board, but it does depend on which particular CDN server you're connected to, and your geolocation. Sometime around that big server crash this year GOG changed its provider (to Fastly). Ever since, some people have found their download speeds tank severely because whichever server they got routed through for whatever reason isn't giving the speeds we once got with GOG.
It might also be your ISP involved too (it may not just be the CDN per se), but the fact of the matter is since GOG changed its provider, quite a few people have had issues.
Yep, since that issue and change I have been getting woeful download speeds, on average 204 Kilobytes a second, where I used to get almost 5 megabytes a second. Been that way for months now. Last tested last night.
My only way around this is to use Free Download Manager 5, with multiple streams per file. That gets me the usual download speed I used to get from GOG.
I only download the Offline Installers and don't use Galaxy.
Due to this download speed issue, my love of and interest in GOG has been waning. I've purchased less in the last few months, especially of games with large files. I'm not fond of having to click every single link either, which I need to do with FDM5, especially onerous if a game has lots of files to download, and especially because I also download MAC and Linux versions.
This is the second time this has happened to me with GOG, and it took many months to get fixed last time. So I am rather fed up. Why I am having to download from somewhere like New York, when it should be somewhere in South East Asia, I don't know.