I've been saying this a lot lately, but Jimmy has really been coming into his own. Like Conan, he excels with sketches and bits, and he's growing as an interviewer. He's still nervous as hell and his accommodating laugh grates me, but he's at least as good as Conan when he's on (though Conan himself is too reliant on the cards).
Plus, Jimmy, like Conan, just seems like a genuinely nice guy who cares for the job he's been given and wants to honor the legacy of his predecessors. To be honest, Jimmy's nice-guy qualities didn't matter to me at first, because you gotta be an entertainer fundamentally, but now that he's growing at a crazy rate I feel so happy that such a cool, sweet dude is excelling.
Oh, and sidebar: THE MOTHERFUCKING ROOTS!