The most obvious change is a redesigned website, which will bring better searching and social media integration. There will also be a redesigned downloader, allowing for faster downloads, and a smoother patching and updating experience for everyone.
Perhaps the biggest news is that GOG will now sell new games alongside their catalogue of PC classics. Indie titles Trine and The Whispered World are already up for download, and Legend of Grimrock is available for pre-order. Future titles will include Machinarium and Darwinia, and there are plans to make AAA titles available too. All of these titles will be available without any form of DRM, continuing the major selling point of the service over rivals such as Steam.