One of the rare runs in comics that gets progressively better as it goes along. Kelly wrote the quintessential Plastic Man story in JLA 65 as well as the greatest Martian Manhunter story arc I've ever read with Trial by Fire. I loved the new additions to the Justice League to his run including Manitou Raven, Major Disaster, and Faith, as well as the return of Firestorm and the Atom.
The only downsides to the run is the unwarented length of the Obsidian Age and the lackluster JLA 100, but other than that I believe it to be the best JLA run after Morrison.