He wants to go out and try other things, good for him. If he wants to do something else, then I think that is great that he can do that. I believe he is going to the late show, which is also a very popular show, so it really isn't a bad move.
Now I've never watched The Colbert Report all that much, but it was a good decision for him as far as his career goes. And I'm sure diehard fans of the show are upset over the move but good for him. In my opinion he is the best replacement for David Letterman. No disrespect to Letterman either, because he's a legend in late night TV.
Stephen Colbert has been on Comedy Central doing the Colbert Report for so long now, he seemed like a veritable institution of the network. For many, it is hard to imagine his show not following Jon Stewart's, and even harder to imagine Colbert doing any other show. But I fully believe that in the end, Colbert will leave everyone in awe of his incredible talent and creativity.
Moving from Fox to CBS will allow Colbert access to more avenues to pursue his satirical comedy and may also give him a new lease of life. Recently, the Colbert Report has faced accusations of being stale and a new format, with a new company may reinvigorate Colbert's comic work.
Stephen Colbert is still wet behind the ears and it's way too soon for him to leave the show. He's only been on air for under a decade, which is not enough air time to be promoted. On the upside, he will be filling in for Letterman, which to him, means a bigger pay check. I know he was ready for a fresh start but many others are wondering why he left so soon.