When I first saw Kisame I thought to myself "Man, I bet this guy is going to be some kind of a bad-ass!" I don't think he's a beast in the fact that he's actually a shark (I know, he looks like one). He's a beast in the fact that if someone stands in his way, he'll completely and utterly annihilate them!
I don't remember exactly the manga, but when Madara revealed himself to Kisame, Kisame sort of acted like he knew Madara pretty well (on an equal kind of level). Bee's pretty cool and I think he'll be one hell of a challenge, however, if no one comes to his aid; Kisame's going to dominate him.