Morrison provided a fresh entry point into the stagnant X-books, and also attempted to push mutants into a larger role within the Marvel Universe. He also introduced some interesting ideas involving Cronenberg-style body horror. There were some mistakes, too, like the way he wrote Magneto as a cheap imitation of himself. But Morrison can definitely "play well with others." There were a lot of weird changes at DC during his JLA run, and he rolled nicely with every one of them, including silliness involving that Electric Blue Superman. And Morrison collaborated closely with three other top DC writers on that amazing weekly 52 series a few years back.
"Injustice anywhere is a threat to justice everywhere."
Martin Luther King Jr., Letter from Birmingham Jail, April 16, 1963
Some of his earlier work was characterful enough, and I was reasonably happy right through Sinestro Corps War. There was the throughline of fear, and Hal's struggle with everyone around him being fearful, the power of fear, etc. But that was quickly dropped, and we had nothing. I just don't feel like we got anything real or significant for "Hal" himself. Rather, we got a universe built up around him -- and shoddily, IMHO, because it all hinged on one thing. It's like if "Court of the Owls" went on for 9 years.
That's a universe thing, and while I complain that we only had ONE thing (the emotional spectrum), and that it was relatively simplistic for what Johns wanted to do with it, I would never disagree that he added that to the GLU, and that it's better for the addition. I just think that at a certain point it TURNED from being a nice little addition to the GLU into a hinderance, because Johns couldn't get past it, couldn't move beyond it. We're 8 years out now from when it was introduced and it's still driving every day story.Also you've complained about the emotional spectrum Corps which was new territory for the Lanterns as it tied energy into emotions then claim he didn't explore new territory?
Most importantly to what we're discussing here, it has nothing to do with the progression of Hal Jordan's character.
As mentioned, he's best known for "Black Panther" over at Marvel, a masterful piece of work, he created Triumph (who you might remember from Morrison's JLA), wrote "The Ray" for a good bit, etc.
If by quintessential we mean "best-selling", sure.
If by quintessential we mean "best understands and illuminates the fundamental appeal of the character/concept", no.
The writer of Black Panther et al prefers to be referred to as plain "Priest" or "Christopher J. Priest", to avoid confusion with scifi writer Christopher Priest.