OK OK hold your horses. First and foremost, a bad movie and one you didn't enjoy at all are NOT the same thing. For example, I find the Godfather boring beyond belief. Does it make it a bad film in my eyes? Hardly, just one I have trouble enjoying at all.
Now, to some of your points, my 0.02:
1. I didn't get the sense that they were locking her in so much as she was. When they leave for wherever (before their death) she is clearly out and about the palace. Elsa, years later, locked herself inside all by herself when she built her castle, so they clearly intended to make a point that SHE as a character was repeating the same mistakes (putting herself in isolation etc). Furthermore during the Do You...Snowman? song sequence you can see her father trying to reach out and touch her, with Elsa being the one to shut him out. The gloves were also a direct response to her panicking. I got a real sense of love and a bit of fear of how to channel her powers to make them her own. Never did I sense cruelty or abuse.
2. How is that even a point? I think what's so enduring is EXACTLY the fact that she stays good, just conflicted. Most people don't turn villainous over being different, just scared (gays, mentally-ill, minorities) I can see how so many people could relate to that over some queen becoming evil and hell-bent on destruction and revenge.
3. She was born with it, as mentioned earlier. Seriously, you're willing to go along that mermaids are real and the fact that one becomes human simply from the magic of the king's wand, yet this bothers you? Hmm...
As for shallow characters? I see a lot of myself with Elsa so I'm a little offended.
Seriously though, I found the characters on display interesting and relevant, with Anna and Elsa (justifiably) being the best of the bunch. I find it odd you found them one-dimensional.