Story
I personally love the Avatar Series and Legend of Korra series for it's story. After hearing from a interview how platinum games worked with the original writers to avoid plot inconsistencies and create a overall better game I expected a story that is similar to a pre-sequel which would have been neat. However this quickly turned out to be the weakest part of the game.
The game is set in between season two and three. A crazy old man who was trapped in the spirit world broke free thanks to the events of season two and now seeks revenge on the avatar who defeated him thousand years ago.
And this one sentence is pretty much all there is to say about the story. It barely introduces anything new to the lore and expects you to watch the series to understand the plot, and it has every right to do so, but you can skip the game and not miss on anything vital which is kinda sad.
Korra doesn't interact with any characters from the series outside of Jinora and Naga (Korras pet). Jinoras interaction with Korra is very lackluster. She will only pop up to give the player a task to fulfill to get Korras bending back, which she looses at the beginning of the game, and in the finale she acts as a reminder of what Korra should already know by now. Which in my opinion is a missed opportunity since in the series Korra didn't have that much character development outside of season 3 & 4. All in all it will take you five hours at most to beat the story mode. It is really a bummer that the story mode came so short especially given how much happens in Season 3 and 4.
The presentation however is really good. Every cutscene is a cartoon like in the series and the animation quality is really good. However there are some cutscenes where I really think that they were kinda lazy by not giving Korra enough frames. From a technical standpoint the game runs at super sexy 60 FPS at 720p on last gen consoles, 1080p on PC, PS4 and Xbone. The cell shading look makes it look like the cartoon and is very pleasing to the eye.

Gameplay
The gameplay is fun but not as complex as other Platinum titles.
This is probably because it's targeted for children but it's complex enough to require some sort of skill to beat. Platinum Games are really good at creating rewarding combat systems.
Here we have a combat system that utilizes light and heavy attacks that turn into combos and blocking/countering enemy attacks like in Metal Gear Rising Revengence.
Every bending element is entirely individual. Earth specializes on short range dealing heavy damage, Air specializes on aoe damage, Water is primarily long ranged and Fire specializes on fast melee combos. You also have to level these elements up as you go through the game. Doing so increases your combos and your Chi. Speaking of Chi it is very important to keep it up if you want to unleash the true strength of the Avatar. To charge your Chi you have to hold down the attack button for a short time and once your Chi is charged up your attacks are bigger, hit for more damage and have overall longer range and sometimes even shoot in multiple directions.
On top of that you can equip different Items before you start a chapter like health potions, revives or even talismans that change your playstyle. For example a talisman that doubles your attack but halves your max HP. Items like these are bought from Iroh's shop where you trade in collected spirit energy that you find along the way. You can also buy new moves to further expand your combo's.
To vary things up a little we have Naga riding sections from time to time which remind me a lot of smartphone and tablet games these days. You essentially tap left or right to navigate Naga who is running on a rail and you have to make sure you don't run into any obstacles. Later you can use your bending abilities to make this task easier.
After you beat the story mode you unlock Pro bending which was primarily featured in the first season. It is really fun to be honest. You and your AI companions Mako and Bolin have to battle the opposing team on a arena in a 3v3 match. Here dodging and blocking is very vital as your AI companions are really dumb and the enemies will get so hard that you and them start playing counter Pong during the hardest difficulty. However it's again a missed opportunity as this mode is ideal for multiplayer, which is entirely missing.