I hated my private school, but would have hated any school, as I'm not a school person!
However, I'm very glad I went, as I still have close friends I met there, there was no bullying, the classes were small (25 in a class) and the range of subjects on offer was better than most state schools at the time. Three separate sciences rather than combined, Latin, ancient Greek, a range of modern languages, a lot of art and music, brilliant literature teaching, and so on.
I think the main differences are the range of subjects (however, I have found a local state school for my DC that offers separate sciences, Latin and ancient Greek), smaller classes, and selective intake meaning students are supposedly more academic (at my school there were lots of rich students who weren't very bright, do not sure the selection means much tbh). My DC's state school has streaming from year 7 and has similarly-sized classes, so we're lucky, but many of the local state schools we visited clearly didn't have the resources or had much more focus on disruptive children and cookery lessons etc. for non-academic children (which might be great for some, but not if you're aiming for an academic career).
My main worries about state schools are knife crime (if a school has knife detectors at the gates and security guards on site, that's a major red flag) and the lack of funds and resources and stress the teachers are under.
I don't think private schools are automatically better, just they have more resources.
State school teachers are deelly dedicated and deserve a lot better conditions and respect.