I'm a fan (and you should be too) because...
Carrie Underwood is awesome. 
It's as simple as that. I don't know how else to put it. She is indeed, The American Idol, by all accounts. Her voice is unlike any Music Artist's that I've ever heard before. I can't help but turn up the radio when her songs start playing.
I can't put my finger on it, and I probably never will be able too, but It's just something about Carrie Underwood, that I just love. Maybe because She appears to be as normal as all of us? Then again, most country stars do. But Carrie does it best, if you ask me!