I personally don't think it's that great relative to other Disney soundtracks. Do you want to build a snowman was really emotional and the best part of the movie. Everyone loves Let it go, but I'm not that fond of it.
I've actually never seen the movie, and never heard the song until now, so I looked it up, and I can tell you that it's likely not that the song is particularly catchy or clever, but it's incredibly powerful. The theme of it is easy to identify with (feeling trapped by the role you're expected to play, rather than the role you wish to play), and the person singing it has a remarkably powerful voice, which projects that power onto the character. Elsa comes off as an easy to like character, because the song is a very elegant way of saying "**** you, I do what I want". It's easy to see why people view her as a strong female role model. I haven't seen the movie, and I already like her.