I have something like 200 games on Steam, GOG, Epic, Battlenet, Origin etc. not to mentioned those from DVD and even CD era gathered from like 30 years. I play very different games, depending on the mood, but if somebody asked me about the bet game I've ever played - this would be it! Intricate world with a rich lore you just want to dive in, check on all those side stories with different endings that are more immersive than many main stories from other AAA titles, glossary for beasts or the potion ingredients, expressive characters, music (recorded with real middle-ages instruments), insane care about the details, voice acting even for those dummy simplest NPCs, wildly satisfying fights, character building options and this truly grim and brutal yet beautiful world, unique homour and a great storytelling among other things - this all adds up to the specific 'witcherish' athmosphere unlike in any other title. You can simply wander across this world even without any purpose and just melt in, you can't get enough and always want to know more about it.
