I use my own install of Piwigo and it handles almost 100,000 pictures easily. Modes like "calendar view" by upload OR creation date help to make finding pictures easy, in addition to the ability to tag photos.
I have been pleased with the product and how it works. There are many extensions available to increase the functionality of Piwigo, but I have not tried anything beyond the "core" Piwigo platform.
I have only had a few technical issues (PHP related) over the 6 or 7 years that I have been using it, and my web host was able to resolve those for me.
The biggest downside (and this is why a 4-star rating rather than a 5-star rating) is the lack of detailed product documentation and the unwillingness of the support community to help "newbies". Most times, I can search the support forum for the topic that I have an issue with and can find record of how someone else resolved whatever that issue is. I have never received a helpful response from the forum. Any time I have posted to the forum for help, I get no response or a disrespectful response from that community.