... it's a game that makes you feel like you're not playing a game.
Many video games are power fantasies, and most that involve warfare depict the glory of combat and put the player in the lead role. Not so in The Witcher 3. Geralt has his own motivations, and he does his best to avoid politics and the larger conflict between Nilfgaard and the Northern Kingdoms.
And CD Projekt never depicts war as glorious or fun. Soldiers describe combat as a lot of boredom and waiting punctuated by moments of frenzied madness. The Northern War of the The Witcher 3 is all about waiting, survival and boredom.