When Legend of Korra premiered, fans were not disappointed when they got to dive back into the world of benders and hybrid-animals, regardless of the fact that they had to say goodbye to the old Team Avatar and get acquainted with a brand new one. Luckily, fans weren't disappointed in that regard either.
Despite not being as popular as Aang, Korra had proven that (while hot-headed) she was fully capable of fulfilling her duties as Avatar when she brought down Amon and entered the Avatar State for the first time. That said, Korra got thrown for a loop when things got turned up a few notches in season 2 - but that's not to say that some episodes weren't still better than others.
Rebel Spirit, Episode 1 (8.0)
Spending all of season 1 in Republic City, it was a nice change of pace for audiences to get to see Korra travel back home to the Southern Water Tribe for their annual Spirit Festival. Unfortunately, upon arrival, things grow heated between Korra's father, Tonraq (chief of the South), and his brother Unalaq (chief of the North).
Things only grow worse when Dark Spirits start attacking the festival and nobody can stop them... except for Unalaq. After demonstrating his 'spirit-bending' abilities, Korra requests that Unalaq be her new mentor.
Civil Wars: Part 2, Episode 4 (8.1)
Despite Unalaq telling Korra that he wanted to unite their two tribes, he contradicted himself by bringing the entire Northern Navy down to the South in order to "unite" them. Unfortunately, Korra's father gets framed and arrested for treason against the North and is then held trial where he is sentenced to death, only for Unalaq to plead mercy and have his life be spared and sent to prison instead.
However, Korra tracks down the judge who was in charge of the trial and interrogates him, whereupon she learns that Unalaq set up the entire thing.
The Guide, Episode 9 (8.2)
After spending some time away from Tenzen, Korra reunites with her old mentor and his family and informs him that she needs to enter the Spirit World. Unfortunately, Tenzen reveals that he's never made it into the Spirit World. Luckily, Jinora steps up and reveals that she has an incredibly strong spiritual connection and offers to take Korra.
Upon reaching the Spirit World, Korra and Jinora get split up and Korra finds herself alone and terrified (reverting back to her child form). A major blast-from-the-past arrives in the form of Iroh who helps show Korra the path to helping her regain her true strength.
Night of a Thousand Stars, Episode 11 (8.4)
One of the best additions in season 2 was the fact that Bolin became a Mover Star (movie-star) and partnered up with Varrick on all of his projects.
During this Bolin-centric episode, thousands of Republic City citizens (as well as the President) show up at the arena to watch the premiere of Bolins' newest mover, only for the event to get ambushed by members of the Southern Water Tribe who plan to kidnap the President and blame it on the Northern Water Tribe. Luckily, Bolin steps in to save the day and outs Varrick as the one who bribed the attackers in the first place.
Light in the Dark, Episode 14 (8.4)
While the season (as a whole) was still stellar, the finale wasn't exactly the best as it left a lot of things open to interpretation for the audience to try and fill in the gaps themselves. After Vaatu and Unalaq combined to create the Dark Avatar, for some reason he grew to several hundred feet tall and attacked Republic City.
Korra, from sitting in the Tree of Time, also grows to several hundred feet tall and defends the city. With the help of Jinora's spiritual powers and Korra's spirit-bending, she manages to vanquish Vaatu and Unalaq for good.
Harmonic Convergence, Episode 12 (8.5)
It was revealed in earlier episodes during the season that there was a Dark Spirit named Vaatu whom the original Avatar had trapped away for 10,000 years during the last Harmonic Convergence. With the event soon approaching, Unalaq attempted to free Vaatu from the Tree of Time so that they would be able to fuse and create a Dark Avatar.
Korra, Mako, and Bolin do everything they can to stop Unalaq, however they fail and Vaatu breaks free. Meanwhile, Jinora's spirit was lost in the Spirit World and Tenzen, Kya, and Bumi, spent the episode trying to find her.
A New Spiritual Age, Episode 10 (8.7)
In the prior episode, Jinora had led Korra into the Spirit World where the two of them got split up. So, while Korra spent the episode trying to climb a mountain and regain her 'true-spirit', Jinora went wandering off and discovered Wan Shi Tong's library (hanging upside-down) and encounters a callback to ATLA when she meets Wan Shi Tong.
However, despite Korra reconnecting with her 'true-spirit, things take a turn when it's revealed that Wan Shi Tong the Spirit is an ally to Unalaq and helps him capture Jinora, resulting in her spirit getting trapped in the Spirit World.
Darkness Falls, Episode 13 (8.7)
This was messed up. After Harmonic Convergence occurred and the Spirit Portals opened/connected to the physical world, Vaatu was released and tried to fuse with Unalaq. However, Korra spent the entire episode fighting him off and trying to prevent that from happening.
Tragically, not only does she fail in keeping them from fusing, but Vaatu ends up ripping the soul of Rava out of Korra (the Spirit of the Avatar) and destroys Korra's connection with all of her past lives. Meanwhile, Tenzen and his siblings get trapped in a Spirit Prison, only for Tenzen to come through and save not just them but Jinora as well.
Beginnings: Part 1, Episode 7 (9.3)
Arguably the greatest moment of the entire series, season 2 decided to send Korra on an amnesia trip, whereupon she (and audiences) got to learn about Wan, the very first Avatar, and how he got his abilities. In a twisting and compelling narrative, Wan receives the power of "bending" from the Lion Turtles and spends several years living among spirits in the Spirit Wilds.
However, one day, he encounters two massive spirits fighting - one light and one dark - and breaks up the fight. Unfortunately, as a result, the dark spirit (Vaatu) gets free and begins unleashing darkness and chaos on the world, which the light spirit (Rava) was preventing.
Beginnings: Part 2. Episode 8 (9.6)
After Wan accidentally lets Vaatu free, he continues to wander about the world only to discover that Dark Spirits have begun to plague the world, resulting in spirits and humans being at war with one another. Wan tries to settle things and make peace, but he fails in his endeavors.
Finally, he and Rava confront Vaatu at the time of Harmonic Convergence and plan to lock him in the Tree of Life for 10,000 years. When the two of them face off against Vaatu and aren't strong enough separate, they fuse their spirits together into one super-being and create the very first Avatar, allowing them to lock Vaatu away.