Steam might lose fight for players in the future, but for sure it will not be to Facebook. Worthy opponent it seems is GOG, they are superb platform with great values behind their offering.
I've only had great experiences with GOG as a platform.
..and I love Steam, too, and both are committed to Linux as a platform for the future. (When is Portal 3 coming?!)
They each have carved out such a great niche and they're each both gamer and developer friendly.. I'm not so sure that FB has demonstrated being either of those things.
