I really enjoy King Richard's prank call style. He's absurd, sometimes obviously pushing for a reaction, but he hasn't lost his humanity. You can tell the dude's got heart and only wants to have a bit of fun with his "prankees". As a weird person who both loves prank calls and probably a bit too much empathy, I really enjoy the bits of humanity that shine through in some of his calls. Sometimes, he'll take time to chat about absurd stuff with an obviously lonely old person, or go easy on someone who seems like they're about to break. Don't get me wrong, he knows how to get an angry person angrier, but it's always in good fun.
Also, I get the feeling he's an intelligent guy. He's quick on his feet, and seems to be aware of a lot of current events - working them into his calls. Not super important, but it's a nice bonus for me.
Points for the nerd cred his pseudonym "Sleve McDichael" grants - originally from an old NES baseball game. I crack up every time I hear someone befuddled by the name.
Overall, a great prank call show.