The GM mode isn't out yet but the first act of Divinity Original Sin 2 is in early access and it's really fun. The only problem is that your saves games get deleted every now and then when they push a big update, but it's kind of worth it for all the stuff they add. The full game, with GM mode, is supposed to hit sometime this year.
I've played DOS 1 a few times start to finish and it's one of my favorites. It's a great 2 player couch co-op (DOS2 will be 4 player) and it's the first game that I thought really got close to the "do anything" vibe of table tops.