Killer Mike has some great flow and lyrics. He's from Atlanta and never got big for whatever reason. His biggest single is a track called "Reagan" where he basically just rips into the political system and Reagan.
El-P is from Brooklyn and was a big part of the underground hip hop scene throughout the 90s. He never really hit it big but had some hot singles and worked with basically everyone that was anyone in hip hop from the 90s and 2000s.
They have three albums together and they're all stellar. I love the first two equally and the third is quite good.
As for Danny Carey. I'm not sure there are many professional drummers that could do what he does. He's special behind the kit. I'd argue he's the best there is right now.