What I think this show does better than anything, and especially any medical drama I've ever seen, is that every character is both deeply flawed but also deeply relatable. Like, every time a character does something that makes you go "why did you do that?" there's always eventually a "oh... that's why." Like, McKay is the poster child of this phenomenon. She'll do a thing that you'll be like "McKay you idiot!" but by the end you totally get why she did it, and you may not always agree but you can't deny she has a point.
My opinion on most of the characters throughout the show was basically a roller coaster, especially Langdon and Santos, who both rubbed me the wrong way in the beginning of the show and only one of them ended the season that low.
I think the only part of the show that really didn't work for me was the subplot with the old guy who used to work on Mr. Rogers. Yes, yes, Pittsburgh callout, I get it, you do this much better later in the show with the Freedom House, here every time it comes up it feels really awkwardly shoe-horned in. The daughter... I don't necessarily know if her acting was bad, or her writing was bad, or that as a person who has lost both parents in my 30's (one to death and one to abandonment) married to a person in her 30's who lost her mom in her 20's, I have trouble sympathizing with a 60-someodd-year-old-person essentially torturing her father because she's not ready to say goodbye yet, as unfair as that undoubtedly is. Whichever it was, she was just annoying to me from start to finish. Literally every other patient-focused subplot at least did something interesting or engaging, or showcased some aspect of the character involved. Even the annoying patients!
Mel is queen. That is all.