The brief backstory was interesting, though I am curious as to who sent Kenny Ackerman for the assassination. Perhaps a further plot thread that might be interesting. It seems Kenny might as well have been Erwin if given the environment but he was truly born into a horrible world; it seems as though the Ackerman family took the brunt of whatever 'persecution' the First King thought was needed. That is what makes Uri unusual; why open up with grief/regret to an Ackerman and in the process make yourself totally vulnerable?
The ending dialogue also seems to hint that masses of people followed the Reiss into unknown plains (before the Walls where raised, I believe) may have been tricked, including the 'special' families. While there maybe be many criticisms that the First King may be subject to, forcing a will of potentially millions of people is truly arrogance.
With that said, Uri (and the First King) seemed certain the world is doomed. It has been a century, so the foresight seems a bit too much. It certainly cannot be something that has been raging for all these decades; a threat that can end Humanity must be brutally relentless or totally inanimate (think dinosaur extinction). With the way the world it set up, either there is a fakenews Mayan 2012-esk event that the entirely of Humanity believe to be coming or it is something from within, a reality that is slowing taking over people, like a plague. Perhaps it is an infection like that in The Walking Dead; i.e. everyone will become a dumb Titan, eventually?
Another interesting note; Kenny said that he needs to inject himself correctly or he may end-up transforming into a Colossal Titan.. perhaps it was dying speculation or maybe there's more to this, why be so specific? Where is the fluid coming from and why are there Titan steroids like the Armor Energy Drink? I think the 'outside' world is pharmaceutically advanced. Heck, even the ODM gear is shocking.. who designed it, who came up with the training regiment, etc. The whole Titan shifting appears to be weapons industry.
Lastly, very interesting the Reiner & Bertolt appear at the concluding moments in what appears to be Shiganshina District. S2 led us to believe that Reiner and Bertolt knew the Beast Titan; it seems almost sure now that he is a commander of some sort. Why else would he mention Annie? And him referring that the 'coordinate' would come to them indicates he is patient and cunning. Ymir said something about scouting 'our strength' when thinking about the Beast Titan, early in S2. He also looks to have made short work of Reiner's hardened outer shell.. wtf. He is trained/experienced in Titan combat and the previous mentions of Reiner being a Warrior, not a Soldier by Bertolt can be interpreted as meaning shifting Titans are like WMDs in an actual war. Beast Titan seems like he is Special Ops. I mean, it looks like Reiner was cannoned down (projectiles like Kimimaro?) with ease. Ridiculous. In the end, him fighting back shows hes the most sensitive of the bunch and is conflict about his actions. Reiner and Co. are stuck in-between a rock and tough place; they've no other option but to become supposed villains. Also, I think Ymir got execution..
The main trio (Eren, Mikasa, and Armin) have relatively bland and one dimensional personas when stacked against Historia, Reiner, and many others. Kenny Ackerman was simply another example.