With The Witcher 3 there was a lot of hype built around it being an open world game, so I went into it expecting something more like Skyrim with less of a requirement to do quests and such. But since it's quite narrative driven, if I'm going for story I feel that I might as well play the original Witcher games first before moving on to The Witcher 3 (if I decide to invest the time in that universe).
Everspace and The Long Journey Home both look like decent space games that I'd like to try at some point. Hyper Light Drifter looks interesting too; I've wishlisted it for now. I picked up Ori and the Blind Forest on GOG a while back and it's been great.
I've just bought some of the recently released Neo Geo games which are fun; I hear that these aren't the best versions of the games, but they're a good example of the GOG team improving the games themselves by adding Galaxy features.