I wouldn't say I am on Team Nurse Ratched, but there are a handful of moments when she's just trying to keep order in a mental institution, and McMurphy is fucking with her for literally no reason, to the detriment of all and the benefit of none (himself included).
Like McMurphy trying to rile up the other guys to watch the World Series and then get all indignant when Ratched tries to tell him she doesn't want to fuck with peoples' schedule. Most of the other patients are there voluntarily (unlike McMurphy, who was imprisoned because he raped a 15 year old girl and then acted like a combative asshole while incarcerated), and presumably just need to be treated for their very legitimate mental health issues. They all seem to be getting along fine until he arrives. Life isn't perfect, but they're doing their thing. Ratched is a ball buster, sure, and goes too far at the end, but she's mostly just a stern nurse trying to do what is best for some very mentally fragile patients. By the time the story ends the only person that is arguably better off is The Chief, but who can really tell.
I don't know. I've never read the book so maybe there's more detail about her there that makes it much more clear that she's out for blood or something. But for a character that is always spoken of as some deeply evil villain I didn't find her to be all that unreasonable for most of the movie.