The ending was rushed and disappointing.
I have 2 complaints:
First, the final level was the easiest level in the whole game. This is supposed a fortress, yet it was the easiest level to get through. Plus, it didn't help that many of the guards just stood there. For example, on the bridge to the lighthouse, there are 3 guards. None of them move (like they are patrolling) and they ALL have their backs to you. Shouldn't they be watching the entrance to the lighthouse and not the lighthouse itself? They were too easy to take out.
My second (and bigger) complaint is that the final outcome is too brief. All we get is a couple of still shots (set in the void; completely disconnected from the city) with voice-over narration telling us the conclusion. I mean, DUH...we already know that Emily will take the throne and the plague will end up being cured (good ending). That is a given. Then the game is over...that's it.
After spending so much time in this world, with these characters...I was hoping for a final chapter or, at least some cut-scenes showing us what happened to the world that we helped create. You know...maybe Emily being tutored by Callista, while Samuel stops by...slowly growing into the Empress. Storefronts being reopened and people in the streets selling their wares. Flowers growing, ships sailing...etc. At least a scene where Corvo and Emily visits her mother's grave (either early on or later in life) and they have a personal conversation about what it means to rule an empire or their relationship (or the possibility that Corvo is Emily's father) or something.
After all of that game play, I wanted to see a world reborn. I just didn't feel a sense of closure and ended up feeling letdown and dissatisfied.