It's based off of an old story called "The Snow Queen" by Hans Christian, and is practically identical to an old Sailor Moon villain named Berthier. There is no brains in it whatsoever. It's being regarded as "The first disney movie to *insert quality here*" in a bunch of stuff, which is almost never true ("It doesn't end in the typical "getting the prince charming solves everything" schtick." -- Like Mulan, for instance? Or Brave?) and despite people hailing it as original and unique, there is literally nothing original and unique about it at all. Plus, the females' character models are the laziest effin' things that I've ever seen (They're all completely identical bases and structures with pretty much the only differences being overall height and color).
Don't get me wrong, I do like the story behind Frozen, and I'm not saying it's not progressive. I like it, and I especially liked Elsa's character because I related with her a fair bit. But, the popularity of the movie is completely overblown and far from deserved, and I swear to god if I hear somebody sing "Let it go" non-ironically one more time I'm going to blow a gasket. There are way better movies, both Disney and otherwise, both in plot and character design and in characterization itself, and that don't owe half their popularity to a single song(which isn't even that great).
It's not a bad movie, but it's not one that I feel is deserving of its absurdly huge fanbase.