Mmmm. Genre defying... or not.
They are a hard rock band (though in today's popular music scene, it's basically considered metal)... however you want to narrow it down. Every metal band does ballads... a song like My Immortal does not make them borderline classical. Evanescence (am I ever gonna spell that right) does not approach their music in any specifically new way. Sure they aren't a rip-off band, but the main reason they're so popular is not because of their originality (though I suppose this is the first huge band of their type in recent years), but because they've gotten their catchy songs to the radio- which propels any popular act nowadays.

No, Linkin Park does not sound like Limp Bizkit. They aren't bringing anything new to popular music though, as rap-metal was popular before them.