My good buddy Ken Levine didn't like Colbert's first show as much as I did but basically we're on the same page: Colbert is a super talent and he's likely to turn this into one of the best late night shows ever.
I disagree a bit with Ken's statement: "One thing about Letterman, from the day he first stepped out onto the stage for his NBC morning show he had his persona down." It always struck me that one of the reasons Dave's morning show failed so totally was that he did it with an attitude of "I'm way too hip to be on between game shows and soap operas."
He had his human side well-protected behind thick layers of snide and sarcastic about absolutely everything. It's the same problem that I think doomed the ninety-seven different attempts to give Dennis Miller his own show. Miller on those programs always looked to me like he was only out there entertaining us because someone was holding his loved ones hostage backstage.
Even when Letterman went on in the more natural (for him) environment of late night, it took him a while to talk to the audience as himself. He hid behind prepared material and he seemed phony on those rare occasions when he said he liked anything. One could argue (I would argue) that he went too far in dumping the prepared material but I think America really began to love the guy when they got a sense of a human being there. That's how I see Colbert's show evolving.