Accidentally caught some of it tonight. He has to pace himself. He was out of breath during his entire monologue, with a lot of jokes about the show getting canceled. Maybe nerves. I watched his pre-recorded bit, which wasn't that funny and switched channels. His band lead is the fantastic Reggie Watts, so he has that going for him. Also he is going against Seth Meyers on NBC, who is a good writer and a wonderful person but has the charisma of a piece of plywood. It is hard to get a good judgement on these shows in the formative stages. Give it a few weeks once the big guests stop showing up.
I still have no clue how he landed the job. He is an absolute unknown here. I only know him through various youtube clips with footballers. Americans for some odd reason drool at the sound of a southern English accent. Possibly that is why he was given a shot. Craig Ferguson was on a fairly popular show in the US prior to getting his hosting job. He had a pretty decent cult following due to his type of comedy and personality, which I highly doubt will cross over with Corden since they seem like complete opposites.