Can someone explain to me why One Flew Over The Cuckoo's Nest is so acclaimed?

Hey, guys! I had been flirting with this movie on Netflix for a while, since the synopsis sounded appealing to me, I like psychological dramas. Tonight, I decided to watch it and it was a huge disappointment. I think the movie was really bad, I'll try to summarize why.

• There seem to be lots of scenes that don't add anything to the story and/or seem totally out of place, as if the director was randomly adding whatever came to his mind. What's the purpose of the fishing scene? Why did McMurphy feel like taking the whole hospital fishing? Some gaming scenes seem purposeless, too. I feel like the movie lacks cohesion and purpose many times.

• The characters seem badly written. Most of them are just... shallow. Many of them receive minimal attention, like some patients or the doctors. Even the patients that do have some importance and get more screen time seem shallow to me, their backstories are not explored and they aren't that important to the plot. McMurphy seems like he's completely purposeless, with an erratic behavior and lack of personality. At first I thought the movie was trying to make us think that he didn't know what he was doing, like a "mysterious genius" or something, but actually... he didn't know what he was doing (lifting the marble stand, really?). The nurse is described on the synopsis as sadistic, but she is really just douchey. I expected her to be much more abusive and mean, she is just uninteresting. The indian Chief is simply forgettable and his sudden change is rather unconvincing. The girls, McMurphy's friends, seem to be the dumbest people in the movie. She goes on a boat ride with fugitives from a mental institution and all she does is giggle? And then, the next day, she breaks into said institution to spend time with mental patients? And there's a second girl who agrees to do the same? And they just sleep there and giggle?? Talk about crazy.

• Some events are just illogical. I already mentioned the whole stupid girls with mental patients thing, but also, if McMurphy wanted to escape, why didn't he do so when he went fishing with the other guys? Or why didn't he climb on Chief's shoulder again and left? And why did he try to escape in front of the staff at the end of the movie instead of waiting until later, since he had the keys on him?

• I feel the movie hardly conveys the messages it was supposed to. The characters do not have very definite personalities, like I stated before, and the whole movie doesn't seem to say much. What's the point of it? What was it supposed to depict? They didn't explore any psychological subject, there was no focus on the thrill of escaping, there was no deep insight into the characters personalities, there was barely focus on the tense relations between patients and staff, there was no depiction of the loss of freedom and the oppressive environment of a mental hospital... to sum it all up, I feel the movie was, like I said, purposeless. I feel like I just watched 2 hours of beating around the bush.

I may have missed the point of the movie, but it was a big disappointment. I'd like to hear Reddit's opinion on it and know why is it so acclaimed. Thanks!

Edit.: Formatting.

Edit2.: Guys, if you're downvoting, I believe you liked the movie. Why don't you expose why instead of downvoting a regular discussion?