Above being adventurous and deserved to be approximately 8/10 ... not as great as the main Avatar ( The last airbender ) some serious errors are there : 1 - lovestory is a way of terrible.They easily fall and sink in love and then break up.And that's not the end ! their mind is still kept with the ex-bf or ex-gf the day after.BUT THAT'S NOT A BIG DEAL I CAN SAY IT HAS ITS OWN STYLE . . . WHY KORRA AND MAKO BROKE UP LIKE THAT ?! I MEAN SORTA WITHOUT ANY SPECIAL REASON.COULDN'T KORRA STAY IN CITY ? SURE SHE COULD!
2 - The last season story wasn't a extraordinary one to be honest.instead season 2 could've been replaced and was capable of the last season ( but opening a new portal was good idea for the end at that place ).
3 - Avatar state wouldn't be worse !! ( no offense ) first that made her sometimes even weaker that herself ( if you say no you have to rewatch the first times she went to that mood ) so we see kinda opposite of what we saw with Aang.FURTHERMORE SHE HAD THE COMPLETE CONTROL OF THAT STATE. AND THAT'S A PARADOX WITH THE PREVIOUS SERIES.
4 - She was beaten by some trivial characters meanwhile she put down Vaatu( which literaly was almost omnipotent ) at the second season.I mean in the last season just catch a glimpse of how she nearly destroyed by Kuvira at the first part ( not even one accurate attack before going to the Avatar state ) !
Except those problems and a little holes in the story that was actually a stunning series to watch.