Well, Kuwait was liberated from an invading force. Iraq was liberated from a dictator who had a loyal following from the Sunni minority.
If you look at northern Iraq, its practically self governing. In fact, we could rope it off and call our job done in that region. However, political reasons keep us from doing so with Turkey and the rest of Iraq. We need the Kurdish state to balance out the Shia majority of Iraq.
Now, there have been problem in the Shia portion of Iraq. This is no surprise since the Shia have a large fanatic fringe. However, the problems in southern Iraq aren't nearly as bad as the resistance from the Sunni triangle.
Basically, we through the baathists out of power. The siege of Fallujah is probably the best thing to happen since the fall of Baghdad since we have killed thousands of militants who would fight against a republic.