It's impossible to explain with words, you just gotta listen.. playing music lays bare your deepest desires, feelings, and insecurities more than any amount of words possibly could. Experienced musicians can easily formulate the kind of person another musician is (like his/her character and upbringing) within the first minute of listening. Whether or not the listener has a connection to the playing is a mutual reflection between the music and his/her own personality.
For me, Arrau doesn't let his technical prowess get in the way of the music and is never afraid to take time and really live in the moment instead of through it, and in a way that the rubato actually makes perfect sense. His pure and introspective character is something that jives with me really well. Some pianists and musicians in general overthink until it becomes a bit contrived and some (well, the vast majority) underthink, but expression is always about finding that balance while being very in tune emotionally. An example of the former is Michelangeli, who isn't so good at stuff like Chopin because his intellectualism and perfectionism get in the way but is really good at impressionism and has a ridiculous tonal color palette. My favorite album of all time is his famous Ravel/Rach 4.