Sounds like a great hard rock song to me. People are like ZOMGNOTPOWERMETAL well get over it.  I think hard rock is the closest you can get to define this song, but it does not define it really, and that is one of the many reasons why I fu%&$ng love this song. Nice video too.
Power metal bands are a dime a dozen. Even when the founders of the genre play it, they get lost in the endless supply. Had my cousin not insisted that I listen to Chameleon, I would have disregarded it as just another clone. I'm glad he did though, as it's my favorite album by Helloween.