http://www.pcgamer.com/divinity-original-sin-2-has-sold-one-million-copies/

Whether or not Divinity: Original Sin 2 is up there with the greatest RPGs of all time is a matter of debate. What's not up for discussion is that it is a big hit for developer Larian Studios. 

That number comes not much more than two months after the game was released. For such an unabashedly old-school RPG, that's a remarkable achievement. Unsurprisingly, the vast majority of those sales came by way of Steam: SteamSpy indicates 921,000 owners on the platform, leaving around—probably a little under—ten percent for GOG.