There are two confirmed paid and full expansions of 10 hour content a la old school RTS style ones, not $1 DLC style. The expansion pass has been available for ages. All other mini-DLC styled content is free. There are 16 confirmed DLC, and the first one was released (temeria armor set, looks cool and has decent stats). Proper mods won't come until they release their devkit, which we have no idea will be when. All that is known is that they will release it faster than the W2 one. Atm all we have are XML edits for stuff like fairer vendor prices or no weight.
Gwent the card game doesn't play like most other card games. It mainly is a single player puzzle pay to win kind of CCG where you just have to resort to ai abuse, tricks and counter picking like hell, because your starting deck is utter shit. And the core mechanic is just baiting resources to win 2/3. It gets really repetitive fast once you have some decent cards. It's rather unbalanced and would need serious overhaul to work as pvp. It is meant to replace dice poker, but in W2 not many important characters could play fist fight/poker. I don't really care for the immersion breaking, I'm all for an extra minigame. In story it is explained that it reached high popularity (like YGO/MTG irl, though way higher social penetration) and there is a quest where you try to obtain rare cards for selling. Maybe if you find card games after giving you some dark grimy quest to be immersion breaking, you could solve that by making the NPC refuse to play, but I'd rather not have such artificial restrictions.
Combat in W2 was better than Skyrim, nearly anything is better. Skyrim is no standard, and W2 was released in the same year, not to mention Deus Ex:HR. Combat is largely unchanged from W2, just a few streamlining tweaks. Just a game of proper preparation.
As for Keira's storyline and Baron's. I'm used to horror stuff from years of gaming, but yeah it's still nightmare fuel-ish.
! The outcome is decided by your prior choices. Baron/wife only dies if you freed the dark spirit back during the dagger contract (or possibly accidently before the main story). I went that route, but otherwise they live because the spirit never freed the children and thus the Baron's wife wasn't punished, not triggering Baron's death either. I was hoping the dark spirit would help me kill the 3 sisters and hey, cool evil horse/kraken monster is always better than ugly evil. Sadly didn't happen.
! Keira's is well, decided mainly on your dialogue choices and how well you know sorceresses in general, especially related to the Lodge vs radovid political games.