Fuguss: I truly dislike their client and they have no offline mass downloader of their own so we have to rely on others to make them for us.
I can't really hold those against GOG because:
1. The Galaxy client is optional, you'd need it only for things where it really makes sense like multiplayer.
2. It is quite understandable they don't want to officially promote the idea of mass-downloading one's games, considering the extra load it would cause to GOG homepages and the download servers (the latter could be alleviated by offering a bittorrent download option, like the Humble Store does), if lots of people did it all the time. At the moment they are merely tolerating it that some GOG users do that.
3. No other digital stores offer "mass downloaders" either,
Overall, to me it is enough that they don't try to actively prevent such third-party tools from working, it would be a shame if they did as those tools are another reason why e.g. I prefer buying my games specifically from GOG (currently 2671 games in my GOG account, plus 77 items in my wishlist).
GOG is the only store I know from which I can realistically expect to download hundreds of games and play them even without the store being around anymore (there may be similar third-party download tools to other DRM-free stores as well, I recall there being one at least for Humble Store but it is only partially a DRM-free store...).
Fuguss: They should honestly have an option for just a messenger client that the games can interface with for multiplayer and nothing else.
Unless it makes the users complain that GOG's client has less features than their competitors'.
Fuguss: While their storefront feels off without the appropriate tags and you can't even filter out demos/prologues/etc. from it and you can actually screw up and have your entire game catalog littered with all these games that aren't even games and you shouldn't even be allowed to add to your collection and should just be able to download.
I agree it would be nice to be able to completely remove demos from one's library, they really are redundant after you have purchased the whole game. This is why I never add demos to my library anymore, even if I wanted to try it out.
At least you can hide the demos (and other unwanted titles), which I guess does the same thing...
Then comes with your issues of games from Amazon gaming showing up as you not owning them or owning higher version of a game doesn't somehow also count as owning the stripped down release of it and so on.
Fuguss: The overall issues with GoG has nothing to do with the service they provide at a fundamental level, their issues are the level of polish they have with their services
Maybe so, albeit I personally can't really say why e.g. the competitors' homepages would be somehow superior to GOG's, and many of them don't even offer forums at all.
To me GOG forums appear to be surprisingly lively and populated, with lots of different discussions and shit (even after banning political discussions), considering how GOG is considered to be a small player on digital game stores.
Maybe I would prefer if GOG used some well-known forum software like phpBB or whatever is the generally preferred forum software nowadays, but to me the current GOG forums work "well enough", especially as they recently fixed the issue that people with many games couldn't access the "forum replies" page, to see easily which threads had replies to them.
If I compare the GOG forum user experience to another web forum I often visit, which apparently uses some forum software called "Xenforo", I actually prefer GOG as that other forum has more annoyances that really bug me.
For instance, quite often when I write or edit my message and try to publish it, it just gets stuck there. If I click the send button several times, it might write several identical messages in succession.
Also, if I start to write a reply but then decide nah I don't want to send it, there isn't seemingly any way (that I see) to cancel that message. It isn't published yet, but whenever I go to that same subforum, it shows that same draft message in the edit field. It doesn't go away until I write another message to that same subforum. That is quite annoying as I have sometimes accidentally sent a message which included both my new reply, and that old draft message (by default the forum software merges those two messages if I reply to another message, and I have to manually remove the earlier message from my new reply).
At least the GOG forum doesn't have shit like that...
As for the polish on GOG store pages, at least adding the review scores to games has been a good move from GOG. Nowadays when I peruse unknown games on GOG sales, it is much faster and easier to make up my mind whether I should considering buying this and that game, by watching the various review scores, and also the GOG user reviews. I recall that experience used to be much worse, I had to pretty much go to other web pages to read reviews of those games and whether I should consider buying the,
If I e.g. see that "Mighty!" icon at the review section, the game is very likely to get at least into my wishlist, maybe even the cart. :) That helps GOG too to get more sales.
When it comes to the Galaxy client, the little I have used it, to me it seems fine compared to Steam, EGS, UPlay, EA etc. At least with light use I don't really see anything inherently wrong with it compared to those other clients. Maybe if I used those clients more I'd start seeing differences but to me they all seem pretty much similar for the basics (downloading and installing new games, purchasing games through the clients etc.).