^He's unsure of himself by design, the idea being that he is ten years younger than the Kirk of TOS and isn't the confident leader quite yet.
Yes, he is young and inexperienced compared to TOS Kirk. But, the problem I have is that he is never shown to be a particularly good leader, someone who can bring together and inspire his crew while providing a stable center. Chris Pine is a fine actor but the scripts he has been given make his Kirk come off as an obnoxious, arrogant frat boy with a high IQ. Not only is he unlikeable to the audience, his crew is constantly annoyed and exasperated by him. His only saving grace is his innate intelligence and bravery but he is not someone you'd want to follow and he seems to always be out for his own personal gratification.
Some of these problems stem from the necessity for the writers to follow through with the ridiculous idea of Kirk being insta-promoted from Cadet to Captain of the flagship. I think ST:XI would have worked better if Kirk had graduated from the academy several years before Nero's attack and was a regular officer serving under Pike who was suddenly thrust into command. There was no reason to condense everything into such a short time span. Instead we wound up with Starfleet:90201.
There is potential in Pine's Kirk but the character needs some much better writing. I could also say the same for the film series in general, it needs to be toned down a bit and take its time to develop a good story. The acting, directing and visual effects are all great but I'm still waiting for a decent story. NuTrek has so far fallen into the trappings of lazy, cliché, big budget action movie writing. The story doesn't exist for its own sake, its just there to somewhat plausibly drive events towards the next CGI action set piece. Again there is potential and definitely more substance than say the Star Wars prequels (NuKirk is nowhere near as grating as Anakin) but every time I watch the new movies, they make me miss the lost art of screen writing.