I am also an old card gamer (at least I buy a new Magic: The Gathering deck now and then) and Gwent seems rather clever and fun
The only thing I don't like about it is I didn't bother with it in the first pub. I regretted this and so at first opportunity, I went back there to play the guy and he was gone. Then I read that you won't get the chance to win whatever cards you could've got from him later in the game (grr).
I think they're gonna patch the game so the quest to get all cards will be completable to schmucks like me, so I guess I'll just wait for that to happen.