I stayed up and watched Colbert last night. Mixed bag. He crushed the Weekend Update style jokes at the desk, his monologue was decent, the show had a ton of energy, but his interviews were awful. Clooney was always a great guest on Dave, but last night he had no chemistry with Colbert. The whole thing was just to set up some silly vignettes. If it's going to be a traditional style talk show perhaps work on the actual talk aspect.
Overall, it was better than a disinterested Letterman, but nowhere near as good as an engaged Letterman with a guest he either really enjoyed or couldn't stand at all. Currently Kimmel is probably the guy I most enjoy in late night, but I consume his content via YouTube clips for the most part as I am asleep before the show actually airs.