I personally had an extremely positive experience in a public mental hospital (in the US). I had a bad psychiatrist at the time who had me sign myself in even though I wasn't suicidal or anything, but that's the only bad part of the whole thing. The rest is good.
The staff and other patients were all very nice and accepting of me. I even felt like I was starting to make a few friends, which was nice. The other patients were just people who were having a hard time, no one was scary or seemed mean. We each had a roommate. We had a daily schedule of activities, like meals, free time, and different kinds of therapy (art, group, individual, outdoors/active), which l liked because I always knew what was going to happen and when. The activities were fun, even the group therapy. The staff members were all really nice and often talked to us about their jobs and lives. Yes, the windows had bars, they took our shoelaces, and some doors were locked. However, there was a common room we could go to freely to watch TV or talk or have a snack, or we could hang out in the hallway, and we were never locked in our rooms even at night.
I was actually taken off my medication there. I think the staff knew my diagnoses at the time didn't really fit my issues, but I didn't stay long enough to find out what they thought. I was released after 24 hours because I wasn't suicidal. It sounds weird, but I'm actually glad I had that experience because now I know that if I ever really need to, I could go there and get help and that it would be okay. From what some people are saying, it sounds like I got lucky, but I'm not so sure because I also know two other people personally who have been in mental hospitals (not all the same one), and they also had good experiences.