in regards to the ending. i just couldn't picture superman and the rest of the gang..losing control of there powers...and superman made a point about BATMAN not making a strategy for himself if he ever turns rouge.
i also thought the fights where super intense when every superhero seems to be on the brink of losing from superman shot to the chest to batman buried alive
About John Stewart: He came up in an awkward spot, he's the third sector 2814 green lantern(Guy is the second) so you already have two characters to work with, while he's black and that makes a different but not to much so. They have since defined him a lot around the JL/JLU character but he's still somewhat meh in a character, he was just the military hard ass and the DCU is filled with those! He feels plain next to the other 3 earth GLs as Guy's the hotheaded roughneck, Hal the first human GL ever and Kyle the new kid with talent.
The thing is he's well defined when when he works with the groups (JL/JLU cartoons and the Green Lanterns Corps comics) but alone he falls apart in ways. If someone could have him defined well as something such as his role of being the planet killer(he's destroyed 2 planets one being mogo the planet GL) or expanding that character more as a hero, I would be glad to see him get more exposure but at the moment I rather have him hang back.