It was clearly an extra-judicial execution. I suspected that from the first news reports and the kill-and-tell books confirmed it. Despite some lip service to that effect, there was never any serious intention to capture him.
I thought it was a shame, too, because we would have been much better off putting OBL and his mooks on trial with all the rights guaranteed to any criminal defendant under Anglo-American law. With all the evidence against them laid out in public, when given their right to speak they would have been unable to justify their actions. And then the world would have seen them as the criminals they were, not as martyrs to their cause.
We did just that with the major Nazi war criminals after WW2 even though they killed orders of magnitude more people than al Qaeda. I always thought that the Nuremberg trials were one of the very few good things to come out of that period. This time around we took the low road, and look where it's gotten us.