Ouch that stings...

In all seriousness, I (like others have stated) don't see how this is anything other than for casual gaming enthusiasts. However; given Facebook's popularity if they wanted to try to compete with Steam and GOG, they have one heck of a foundation for which to play with..

Somehow I don't think this is going to cut into GOG's demographic. And Steam is so big they'll probably barely notice, unless this proves to be a really huge success.

I don't think the casual gamer market is that big.

I think everyone with a cell phone could be considered a "casual gamer". Look at the recent success (and failures) of the Pokemon Go Augmented Reality craze.

What's not big right now is the VR market, but the amount of content (although like any new medium, has repetitiveness due to people latching onto a successful recipe), is growing almost daily.

Maybe we have different definitions of "casual gamer", but to me, it's anyone with a mobile device who isn't a hard core PC game player, but someone who still plays games as a distraction to pass time they would have wasted doing nothing at all. (Although I really appreciate Amazon Kindle.)

new heaven for microtransactions

As much competition as boardgames. Unless they offer installers for the games you bought they are not interesting; just another Steam (without Steams experience in the "big" game sector and without Saint Gabe, the saviour of PC gaming).