Story, characters, art direction, combat and action, 3d animation. This show top quality on every level...and OMG those freaking facial expressions are insane.
Riot did for Arcane what they did for every project they invest in. They take the best ideas from the world's best in a specific field. Then, they hire the people with the right skillset, give them a limitless budget with no time limit to develop something that compete with them on first try. They still have a 100% success rate at this.
This show is easily in the same league as Pixar and Disney quality wise. I would even argue that it makes them feel a bit shallow since Arcane has it's own style and art direction. It's beautiful, fresh and, again, those facial expressions are really something. Also, for those of you who are not aware of Jayce and Victor in game character story, you can't understand how good it's gonna get. With the amount of care seen in in the first 3 episodes, I can 100% guarantee you that we have yet to see the best of this show .
(English is my second language. Sorry if I sound unnatural sometime.)