First of all, I was genuinely impressed with all of The Ultimatum. Not only did it tie in Bolin and Mako's family, but it really gave the sense of urgency. It was the first episode I have seen in any Avatar season where I felt concerned for the characters. Tenzin's last stand was beautiful, but unfortunately, it wasn't his last stand. I understand that people didn't want him to die, but I feel like it would have been the right move. Tenzin has served his purpose already by training Korra and reviving the Air Nation and Jinora was proving herself to eventually take his place. Not only would his death be significant with Korra, it would be significant to the would and would show the great lengths the RL would be willing to go to. Tenzin was NOT the RL's only leverage, considering they had all the other Airbenders, so his death would have been the logical choice.
Kai, should have also died or at least been significantly injured. He sacrificed his life for the others, redeeming himself for his past mistakes and proving that he was a true Airbender. I suppose his survival was only for plot convenience though.
I was also convinced that Lyn or Su were going to kick the can or Toph was going to be involved. With all of the time spent developing their characters, I thought their would be something significant with that family. Especially when Lyn told Su that she loved her right before battling P'li.
Lastly, as far as deaths are concerned, I really with Korra's dad would have died as well. Died while protecting his daughter. How perfect that would have been. Unfortunately, good guys can never die and it takes away a lot of the impact that it could have had. Korra would have been rightfully traumatized had her dad and Tenzin died because of her. Now, I'm not arguing that I like to see the good guys die, but in this instance, it would have been particularly devastating if they would have offed a few of the major characters. They have already shown that the RL will do what it takes to further their agenda, so why did the writers hold back so the good guys could conveniently survive?
Anyway, Pli's death was warrented since Zaheer needed a way to let go of his Earthly attachments, but I wish the others would have survived to carry on into the 4th book. I know that it was stated that every story arc would be self contained, but they also only planned once season initially. This had the makings for a 2 book story-line. The RL was not fleshed out as much as I would have liked. I wanted to see more character development from the others to get a clear idea of their personality. Ming Hua was pretty wreckless, though, so her death fit her character. But I just can't understand why Ghazan killed himself when he could have escaped as easily as Bolin and Mako. It was such a waste.
Finally, I am very confused about what the RL wanted Korra for in the first place. If they wanted to be her elemental masters years ago, what changed now that they wanted her dead? It seemed like they wanted to kill the Avatar all along, so Zaheer must have lied about wanting to train her when she was young. I was expecting something more elaborate than just ending the cycle.
All in all, I enjoyed the season for what it could have been. It had potential in my eyes and I will just have to imagine it slightly differently