The Legend of Korra had a lot of promise, but overall there were just too many flaws to make it a good show.
There's almost not character development for the main cast. Korra starts off impetuous and bullheaded. She rushes into things without thinking about the consequences. She readily uses bending to get her way. These are pointed out by flaws in the very first episode. She ends the season exactly the same without these issues ever seriously being dealt with. Mako starts off as a quiet, boring character who's a bit of a jerk, and ends the season exactly the same — with no non-superficial explanation for why two girls are after him. Bolin is basically just comic relief, his emotional pain used for laughs and then forgotten. Asami has a bit more depth, since there's an ongoing story where she actually has to change somewhat given her father. Pabu and Naga barely even have personalities (which is quite a contrast compared to Apaa and Momo. Some other characters have a bit more development. Tarrlok is one of the more developed characters. Yet some of his actions seem to serve no purpose unless he was actively trying to help Amon.
That leads us right into another major problem with this first season. A lot of what happens seem heavily contrived. As if the plot is on rails and characters aren't allowed to think or act naturally to what happens. The security forces are effective, until they need to fail and then they are the worst security force ever — not just losing, but not even noticing anyone approaching them or audience members pulling out weapons. After the Avatar is kidnapped, Lin suddenly knows where the bad guys probably are — Why didn't she go after them a long time ago? And combat, though animated well, is full of tactical fail. Earthbending holes under the mechs or rock armor or any number of other things would have made the fight more even. Later similar techniques just seem to be more effective for no reason. Combat in At LA
was more clever than this.
There's also a failure to examine the themes that are raised. Are benders lording it over non-benders? Korra seems to indicate it might be a problem. Maybe Amon has a point. Korra's lack of thinking and flexibility seems to be a problem too. What about the philosophy of airbending? These are brought up but never examined.
Hopefully season 2 will be better