As a long time Dungeons & Dragons / Table Top RPG player and game master The Witcher feels like a BECMI Dungeon Master’s really well developed home brew world. Very high praise. Like in BECMI the Elves, Dwarves and Gnomes feel like classes and occur spairingly. Like in BECMI religion is a thing but not much a part of the story. The brilliant bit is the whole Witcher orders creation and openly and actively hiring monster hunters.
I also like what seems to be elves are not these Tolkien beautiful angelic beings. Most of the elves running around in human society are beautiful but not most elves hiding in the hinterlands or “squirrels” raiding human society.
Somewhere I’ve read that 0-5 level characters are still in the normal human ability so in The Witcher there are “mutated” characters with level 5+ abilities.
Magically speaking maybe not so much BECMI but ODD with a very forgiving GM with on the fly spell creation. Signs work as traditional DnD spells and cantrips.
Using portals and the world spheres colliding to bring what are often time nonsensical and contradictory fantastic creatures into one world was a great idea not used as much since the 80’s.
I do have one complaint both time and distance feel much like a good DnD campaign, it only matters when it matters but in fiction I find myself lacking a good understanding of place. And place or Kingdoms and cities do seem to matter. Lots of good world building is being lost on my inability to link it all yet.
Disclaimer: Currently I’ve read Saga 1, 1/3 Saga 2, Last Wish and a couple chapters in Swords if Destiny. Watched the first season of the Netflix Series and caught a few YouTube videos on the books and games.