The GOG Mixes feature always seemed like something half thought out and half implemented which over time seems either intentionally or unintentionally to have become obscured or otherwise made difficult to discover/use as if they were trying to say "We regret having made this, what is our exit strategy on this feature." or something. :)
I've made a few GOG mixes before but there isn't anything anywhere in my account pages or elsewhere on the website that I'm aware of that I can click on and see "GOG Mixes you personally created" nor any way to "follow/unfollow" them, nor to like/unlike/dislike them nor comment on them or other standard social media features.
The lack of discoverability features, search features, social networking features etc. in GOG Mixes made it almost completely useless IMHO. I say this because any purpose they currently serve is a use case that is almost certainly done better off-site on a Google Docs spreadsheet, a Blogger.com blog, wordpress blog, personal website or some other mechanism that at least gets seen by Googlebot et al. Also the game list creator would have maximum flexibility with regards to the display of information and other features etc.
Anyhow, as soon as I concluded that this feature was abandoned and most likely to get axed by GOG rather than fixed some day, I stopped bothering to use the feature. That wasn't hard to do because it doesn't really show up anywhere prominent on the site from a UX design perspective anyway.
There are some people who have used GOG Mixes to create lists of games to share with people for one purpose or another, but the existing GOG web code and features for this leave it the least desirable way to share lists of games with others IMHO. I'm kind of glad it is being officially graveyarded.
Someone could literally make a custom Wordpress theme in a few hours and offer it up for free download or whatever and replace the GOG Mixes system with something infinitely more user friendly and useful, even though it wouldn't necessarily be centralized anymore. But the lack of any real useful search or discoverability feature in the GOG Mixes system didn't make it useful that they were all hosted on a single site anyway.
IMHO what would be much more useful is a generic way for everyone to create GOG Game Collections, have the user interface for how to do that built into the website and Galaxy in a prominent location and not buried/hidden, so that people know it even exists, have social networking features (like/dislike/commenting) available but also configurable so they can be entirely disabled if one so chooses, and have a way for people to share their collections in their status feeds so others can discover them, as well as having a "My Collections" category on one's profile page - again for discoverability, and to have some easy to find search feature for people to be able to search for collections also, rather than the search being "Go to Google and type in site:gog.com <keyword>" which is crap.
So I'd rather either see no such feature exist at all, or if it is going to exist then I'd like to see it be something that has an actual end-goal put into its core design, and then all of the steps taken to reach that end goal and be useful both for us and for GOG, and with a good user interface and functionality. The GOG Mixes feature seemed to be something done more of a whimsical bottom-up design with no real end goal, and no commitment to get anywhere with it over time, so it never became terribly useful, and I think most users don't even know it exists at all anyway.
Until they make something new and superior available, IMHO we're better served by the suggestions I made above or even hand writing a list of games on a piece of paper and uploading it to imgur is more useful. :P