I haven't played The Witcher 3 yet, but a lot of people who have have told me that the Gwent card-game-within-the-video-game is awesome. The last card based mini-game I played was Pazaak in Knights of the Old Republic, and that shit sucks.
My friend Alan picked up the Hearts of Stone expansion for Wither 3 on PC, and it happened to come with a pair of Gwent decks - Monsters & Scoia'tael (The Nilfgaard and Northern Realms decks were available with the Xbox version of the base Witcher 3 game).
Gwent is played over 2-3 rounds, with the winner being the first to two wins. To win, you need to have the most points on the board by the time both players have passed.
The game begins by the players selecting a leader card for their faction, each with a different one-shot power - examples being draw an extra card at the start of the game, or once per game return a card from the discard pile to your hand.
Each player draws 10 cards from their deck and that forms their hand for the rest of the game.
During the game rounds, the players take turns either playing a card or passing. Once a player has passed, they forfeit any further turns, and the round ends when their opponent chooses to also pass.
The cards come in 3 broad categories - creatures, weather effects and actions.
Creatures are placed in one of 3 ranks - close combat, ranged combat and siege combat. Each creature card comes with a points value, a rank it must be played into, and it may have a range of special abilities. Hero creatures are immune to the abilities and effect of other cards.
Weather effects cause all creatures (both players') in a particular rank to have a points value of 1, and the various action cards can do a range of stuf, like dispel weather effects or kill all of the highest points value characters in play.
Once both players have passed, points are totaled up and playing field is cleared. Importantly, no new cards are drawn. You just have to keep playing with what remains of your hand.
In the game that Alan and I played (my first game ever), I over extended myself in the first round, using up too many of my cards and leaving little in my hand to continue the momentum of the first round. Alan revealed that he had goaded me into doing that, and so to celebrate that new insight I allowed myself to be goaded into doing that a second time.
One thing that I couldn't help but notice was that there's only one siege card in the whole Scoia'tael deck, and in our games I din't see any in the Monsters deck (though there are 3 or 4). Alan mentioned that the other two decks are much more siege-heavy. I feel like this set suffers from that lack of options, and I'm a bit saddened that there appears to be no way of getting the other two decks outside of paying an absurd amount on eBay. Perhaps someday there will be a retail release of Gwent in it's entirety, but that's probably just wishful thinking.