Basically, we didn't really learn much other then the Ethereals were testing us Humans just like they did to all other aliens under their command where if they fail to have the gift, they will be their ground troops. Ethereals are also cursing themselves for not having the proper gifts to ascend. So they say they are the biggest failure because they thought they had the most potential. Instead they are relegated to the task of looking for the 'Chosen Ones' that will eventually surpassed them to ascend.

Your volunteer that sacrificed him/herself was supposedly the Chosen one of the human race because of the potential after using the Gollop Chamber (unlocking Mind Rift) but died. So I think the new DLCs will be the about looking for the replacement Chosen One and the aliens will be looking for him/her as well.

I think that just mean that the war didnt end, and also, by looking at the achievements, you'll notice that there are a few achievements that is not possible to unlock with the current game that is based on some scripted missions.

Not to forget they kinda dump the whole Outsider idea, after you get the Hyperwave Relay. Then, focused on finding the Ethereals. The story does feel a bit unfinished when the conflict between Shen and Vahlen sparked when Varlen supports the idea of Psi Soldiers. It does feel that it will be an interesting conflict to explore later on, but sadly, it ended abruptly.

I also find Brandford, Shen and Vahlen to be rather interesting characters. It just needs to be expanded even more.

Yup, I like how there was some tension built up by Dr Shen and Dr Vahlen. But no fruit. The Council also very quiet and almost not a tweet from them when the Temple ship appeared. Panic levels also did not rise to simulate widespread hysteria. And we landed on that ship like a boss... they should've made it harder like taking out other bases giving shield transfers to the temple ship, take out patrolling UFOs etc before allowing us to board the ship.

I think maybe if there wasn't any initial build up of characters, we would not expect more. But the story given was a bit half pass. At least the original enemy unknown showed some closure after the Cydonia mission.

Is Cydonia suppose to be the last missionin the original game?

Still, i think the story hasnt end yet, as i dont think the Temple Ship is that easy to beat, except the 2 Sectopods part. It does feel like it was rushed, though, as the Temple Ship mission is even easier than the first few mission.

Your tech has gone far beyond what could have been in just a few short months. Plasma, Lasers, Invisibility from the ghost armor, the firestorm interceptor nullifying the millions of investments put into flight as stated by the chief engineer. If you fail, well then, humans weren't meant to evolve past the ethereals.