The best thing I find in this game is a comparably low entry threshold. I was unfamiliar with Gwent in Witcher 3 because I never played it (wooden PC) but this Gwent came to me as intuitively as it gets. I didn't have to spend hours on the forums and equal amount of time in the game trying to figure out how things work. Another key point is that the F2P system is not abusive towards players that do not plan on investing money in microtransactions. You can get literally anything in the game without paying a single coin. Yes, this will require tons of grinding and swweating, but you can get there. Last but not least. If you get your deck sorted and tune your stategy well, you can beat anyone, including the guys who invest tons of money into additional top cards (which you can get for free anyway). Gwent is not about having all the top cards, but finding the best way to utilize the ones you already have. That's how you implement F2P system perfectly, if you ask me. P.S. Ze goodest cards design mesa has ever seen!
