Spoilers: This episode answered some of the remaining questions about the relationship between River and the Doctor, namely that she was, in fact, in jail for killing the Doctor, and that the two really are married.
The twist is that he isn’t really dead. The Doctor’s experience with the Silence has convinced him that he had been meddling in the affairs of the universe too much, so in order to protect it and himself, he goes into hiding. This means that River is protecting the Doctor by staying in jail for a crime she didn’t commit.
What we didn’t see happen was the fulfillment of the prophecy ‘Silence will fall when The Question is asked,’ though we did find out what it means.
The Silence is the Doctor’s silence, that is, his death.
The Question was right in front of us the whole time, Doctor Who?
This implies that the next series will delve into secrets of the Doctor himself.
Of course, we’ll have to wait until autumn of 2012 to find out.