I tried it briefly. I have never played any of the Witcher games either, but that didn't bother me.
It's like, sure it's fun and all, but there is only so much time I have to allot to leisure activities, and I ended up setting Gwent aside for now. Certainly worth a try, and distinct enough from other online collectible card games to have reason to exist.
I think I ended up playing more Hearthstone over it due to Gwent's slower pacing, at least according to how I perceive it. I remember not being bothered by game pace when playing War of Omens.