Ok so I don't browse the forums a lot so I have no idea if this has been brought up before but I recently spent a few days, yes days, going through the 700+ games in my library checking for updates and found at least 54 of them had updates I was never notified about including one game I just recently purchased. This is the second time I've done this though last time I only had maybe about 100 or so games. I'm not sure what the deal is with GOG's update notification system but I would like to offer a few suggestions as to ways to improve it aside from actually making sure a notification is displayed when said games are updated which should be the first thing to fix especially for games like The Witcher 3 which was also among the list of games I was never notified of updates for. You would think at least that game would have given me a notification when it updated last at the very least.

1. Add a sorting option to sort by recently updated and make sure it's accurate. This is something that humblebundle.com does with the library and has been essential for me to make sure I have the latest versions of my games on their site. Being able to quickly sort by recently updated will allow people to see all the games that they need to update at a glance so even if they managed to miss the update notification they can still see what got updated at a glance.

2. Display "Last Updated" in the file list section. Yet another tool that will help in identifying when a game was updated and also something they do at humblebundle.com (in fact they do it per file and not for the game itself). Sorry to keep bringing up another site but I figure it would be handy to use an example of it already being done to give people an idea of what I'm suggesting and how ti can be usefull.

3. Provied per file hashes for files on the site. This isn't necessarily an update thing but more of a file verification method for people who still use the site to manually download their game files and can be a useful tool in double checking already downloaded files to make sure they haven't been corrupted in any way. This can even be done as a separate page much like the GOG Downloader links are so as not to clutter the main file download area. I know technically you can just use GOG Galaxy and it will verify the files it downloads but with the point being to have GOG Galaxy optional it would be nice to have a way for people to manually verify their files outside of Galaxy or any of the third party tools. Right now I'm still using the GOG Downloader where I can and for what I can't either manually downloading files that are small enough (and hoping they download correctly) or using GOG Galaxy for the larger files to be sure they are downloading correctly and don't get corrupted since I'm sure Galaxy, like the GOG Downloader, are hash verifying the files it downloads.

Any way these are just a few things I think can improve the overall quality of the site and give people confidence that what they have is the latest available even when the update notification system isn't always working as expected. Feel free to add your own suggestions and critiques to what I've mentioned here and hopefully we can help improve GOG a bit for everyone. I care about this site and I want to see it do better. I'm not blind to some of the crazy decisions that have been made on here but they haven't gone so far as to effect me as much as they have others but I feel like if we speak out and try to offer better solutions that maybe we can make things change for the better. After all without us there would be no GOG.

I feel your pain, but we already told GOG similar suggestion for years.
They don't seem interested in improving the site very much : (