I can understand why people would be upset, but I think that its a good kind of an upset because this was in a lot of ways a beautiful death of a key character.
Ever since the start of this series Kanan has grown and changed as a character from tortured ex jedi, to unsure mentor, to a father figure, and finally a hero.
When we first met Kanan all we knew was that he was a jedi who blamed himself for the death of his master during the Jedi Purge, he didn't want to be a hero or really even a jedi anymore. But as he took Ezra under his wing he realized that he knew so little about not only the force but the place of the Jedi. He went though amazing growth, he didn't want to be a rebel, I think he was a guy who was weary and tired, but fate intervened and he became a extremely likable and positive character.
And then he did the only thing he could do which is die.
This whole episode was beautiful and strange to look at because they went out of the way to mute the colors.
I loved the tie in with Rogue One as Thrawn's pet project and the reason why the Empire was on Lothal was getting a possible funding cut to support Krennic's project Star Dust, the Death Star. so Admiral Thrawn had to return to Coruscant and had to leave Pryce in charge. There's been a rift between Pryce and Thrawn for a while, mainly due to her being fairly incompetent as a military leader.
We get another cool link to ANH when we finally see what the Interrogation droid does. Basically it shoots you up with a hell of a truth serum.
The rescue plan was neat using gliders to make a stealthy approach. But as always the plan goes awry soon after and during the excape, Not only do they encounter Ruhk which costs Kanan his light saber. But we finally get something that I'm not sure I agree with.
Lets be honest, we know that Kanan and Hera have been circling around the whole love angle for a while. And while her truthful statements under the influence of the drugs was cute. Having her finally tell Kanan that she loved him under the drugs was a odd choice for me writing wise.
Anyways, Pryce being the idiot that she is decides to destroy the fuel cells that are attached to the Tie Defender Factory to kill the Rebels.
Kanan in a ultimate show of self sacrifice holds off the explosion with the force while pushing Hera and the escape shuttle away.
In a completely heart breaking moment though, the last thing we see is Kanan looking at Hera and his eye's clear up completing a promise that he made to her after being blinded that he would see her again. Then he was consumed.
Then we get a really nicely done end credit with ashes falling.
What's really nice about this is it starts to lockup a lot of story line questions.
Why weren't there Tie Defenders at Yavin? Because Pryce angry at the escape destroyed the factory. You can bet that part of Thrawn's fate is going to be tied up in Pryce's fate and he's not going to be happy
Suddenly with a blast the mission on Lothal basically ends, there's no more factory, and no reason for the Empire to really stay there. This nicely sets up the final four episodes maybe not staying at Lothal.
this also takes Kanan off the board and reduces the number of Jedi left accounted for to one, and that's Ezra.
We know that we're heading towards a major fight now, but this episode is a punch in the gut and really shows that Filoni and Disney are really able to up the emotional ante in this series