The best analysis I've seen thus far on Zarqawi's death is from from Back to Iraq 3.0. Chris has been pessimistic about the future for Iraq, but he is cautiously optimistic today.
It's not just, or even primarily, the death of an evil man. It's the 17 raids that occurred at the same time. It's the appointment of a Sunni minister and a non-militia Shiite minister. It's the way he was apparently killed, as part of a bigger painstaking process of isolating him and boxing him in. It's the suggestion that Zarqawi was betrayed by Sunnis that had come to hate him, and were ready to strike a deal. It's the belief that many Sunnis wanted to deal, but were afraid of Zarqawi's vengeance.
I've read a claim by historians that there's a time in many conflicts when the parties have worked through their initial enthusiasm for murder, and are ready to reconsider their goals. I remember when this happened in Lebanon, after a long civil war.
On another front, it is said that both bin Laden and Zawahiri had likely come to hate Zarqawi and that they will celebrate his death. Perhaps true, but the hunt for Zarqawi took up a lot of scarce military and intelligence resources. Now they will be redeployed.