jeremy.d20: Well, OP here. It's been 2 and a half days and I just went through all the reviews again. Mine still isn't shown, even though the "My rating" field at top shows that I gave a 2-star review.
I did use the word "rape" in the review, while discussing part of the game involving an attempted rape of one of the characters. Maybe the review got filtered because of that. Either way—censoring, lack of feedback on moderation, or just a VERY slow system—it's pretty disappointing. The reviews are sorted by "helpfulness". So new reviews, which are marked as helpful by "0 of 0" people, are in the middle.
GOG has categorically stated both publicly and privately via support repeatedly over time that they absolutely do not screen nor filter reviews. I've personally come to the conclusion that any quirks that we observe of this nature in the system is quite frankly explained by the system being wholly inadequate and poorly conceived rather than malicious or with some behind the scenes conspiracy going on.
The review system is just complete useless crap IMHO, at least from my personal perspective. I hope some day that they will replace it with something much more modern using elements similar to Steam but perhaps not copying Steam 100% as there are some elements of the Steam review system I'm not completely fond of either, but despite that I personally use Steam's review system as my first stop when garnering public sentiment about games as there are a lot more volume of reviews, a lot more controls in place to keep relevant reviews in eye view, a combination of long term review visibility and recent popular reviews giving a balance that includes NEW reviews, and various other useful elements such as whether someone owning the game and how many hours put into it, whether they are playing the early access or final release and other factors. GOG's system on the other hand is just as gameable if not more gameable and corruptible than the forums are.
I recognize that I'm being blunt and harsh but truthful about this and I say it like a big brother with love towards GOG rather than as a kick in the face. Eventually they will allocate resources into replacing the ancient crappy review system with something useful, but not until they have no higher priorities I'm sure and they probably will have their hands full of other higher priorities for some time to come I have a gut feeling. In the mean time however it doesn't bother me in a huge way. I simply ignore the review system largely and use Steam, Metacritic and other sources and aggregate what I find into a picture in my mind that is more useful at least to me personally.
In closing, I can say that I've written several reviews in the past that never showed up at all for a week or more then when I went to look and went through page after page endlessly I eventually found the review after n days. Asking GOG about it they said something like "that shouldn't ordinarily happen" or something like that, which implied to me that sometimes it can happen extraordinarily, which is certainly what I was observing. Then again I seem to have a knack for finding problems with GOG's website that "ordinarily shouldn't happen" and often which nobody else can reproduce. GOG probably lovingly thinks I'm on crack for months or years or more and then magically one day they update something and the problem is resolved. Happened to me many times in the past. The review system has problems of this nature. Nobody will acknowledge them likely but they're there and I really don't think any of it is intentional. Never explain to malice that which can be explained by lack of human resources and priority. :)