Emma Frost, at least in the comics I've read in which she appears, is an all-out male fantasy, and she's a character conceived with male readers in mind. All I think of her is that she's the archetype of the femme fatale, and the archetype of the bad sexy girl who takes the hero (Cyclops) away from the good naive girl (Jean).
She's not a bad character per se, but not exactly a character for female readers, and she certainly would be written very differently if I, a woman, were the writer.
Keep in mind, heroes look good because they look the way a male reader fantasizes he could look. But heroines look good because they look the way a male reader can fantasize about being with them.
We women perceive the difference. When we see a comic with constant ass-shots and boob-shots, or simply when we see a female character always giving the come-hither look or striking oddly elegant poses... we know there's a difference between how she is, and how the stern grimacing male hero is. We know they're not the same, we know the reader is supposed to wish to be the hero and to wish to be in bed with the heroine.
Because of this, we can't identify. And because of this, most of the comic book readers are males, and yet the industry keeps wondering why.
Plus, male heroes are free to look unconventional sometimes. There's the Blob and the Toad, there's the fact that Deadpool is actually ugly under the mask, there's the Penguin and Clayface and MODOK etc. etc.
Unconventional female characters aren't really allowed.
Here's a female character I can appreciate:
Squirrel Girl. She's cute, but she's not sexualized: just what a female reader usually wants. A female character that is a power fantasy and is cute enough that I'd want to be like her, but who doesn't thrust her crotch in the reader's face.. wait, so isn't this just what male readers get with all their all male heroes?

I find her one of the best superheroines.