This will be interesting for a number of reasons, here are the key features:
- Client is fully optional
- Client allows you to "Cross-Play" with anyone regardless of the platform they've purchased a game on (e.g. playing with a friend who bought the game on Steam whilst you bought it on GOG.com)
- Online activation is not ever required (multiplayer and downloading the game itself obviously requires internet connection)
- Achievements supported by client
- Updates supported by client
I'm not sure if anything else was fully "announced", as they were rather vague on the whole thing in my opinion. I'm guessing there will be some sort of integration of a Friends system and the Community/Support already included on the GOG.com website, although both of those ideas are purely speculation.
Again, if anyone has any more information please post it.
(Article promoted by Andytizer)