The episode was great, and I loved the Polis story line, but things felt incredibly rushed in some aspects. And The Arkadia story line is an absolute mess right now--mostly, it seems, due to it feeling rushed.
Bellamy is acting incredibly out of character right now. He caused all those deaths, yeah. Then he shed a tear or two in front of Kane. But he didn't actually show any major reaction to what had happened--he didn't trash his quarters, he didn't snap at anyone, he didn't collapse, and he did absolutely nothing to justify his sudden xenophobia in relation to the story itself. He was lovely one moment, and the next, he's slaughtering an entire army of Grounders sent there to protect him and the Sky People, after having shots with Post Apocalyptic Hitler™? This doesn't seem like Bellamy at all. Bellamy would have marched on the Ice Nation itself. But if this is the new him--I have to say, I've officially reverted to hating him as much as I did in Season 1.
Now for Pike. Is his sole purpose just to fuck things up? Because that seems to be the way the writers are taking him. He's incredibly one-dimensional--wah, look at me, Ice Nation killed my people so now I'm a xenophobic douche--and his election to Chancellor was incredibly anticlimactic. He almost causes Lincoln to get beaten to death by angry rioters, gives a little speech in front of a couple dozen people--if that--and then gets locked up after he tries to lead a strike on the army Indra's leading. Then the elections are held--none of which we see or are a part of--and suddenly... He's Chancellor? What are the people thinking?
As for Nia... I know it's great that Lexa finally got her revenge for Costia, and her threat to the throne is eliminated, but... We just met her? I'm not necessarily complaining that she's dead. But perhaps her death could have had more... Buildup? Perhaps we could have had more backstory, in the form of either flashbacks or direct storytelling.
The Clexa scene in the end killed me, by the way. It was relatively short. But it was wonderfully composed and we finally got to see Lexa's awesome back tattoo! Considering Jason said she got it in the 3 months since Mount Weather, I'm wondering when we're going to get an explanation about it--what it means, why she got it, etc.
I think I can understand why the writers tried to cram so much into one episode--they only had a set number of episodes they could utilize, I think--but taking things a little bit slower would have been a good idea.
TL;DR: Post Apocalyptic Hitler™ and Bellamy are rushed and being stupid as hell right now. Nia's death needed more backstory. Clexa is great.