GOG.com announces their support of old games is mostly ready for Microsoft's new operating system. They explain how users can help improve compatibility, and describe where things currently stand:

Today, roughly 85% of our library is labeled as compatible with Windows 10. These games were fully playable with no significant performance or graphical issues during our testing process and are ready to go right now. You can filter through Windows 10 games in our catalog, and the compatibility will be labeled on every game card.

Moving forward, we plan to continue our work to bring as many of the remaining games as possible over to the new OS. As new updates and features are released, we hope to see improved backward compatibility and new tools to work with, but it's always possible for new issues to come up along the way. If you do suspect that a game should not be labeled Windows 10 compatible, we'll appreciate your help in getting to the bottom of things, but you can always rely on your 30 Day Money Back Guarantee.

The most important thing to stress is that Windows 10 is a brand new operating system, and that means we're still in the middle of a transition period. The coming weeks or months may be rocky as the first wave of patches hits the OS, so we'll constantly monitor the situation to quickly put out any fires.