The expansion of the universe with the other Lantern Corps is, in my opinion, one of the best things that ever happened to Green Lantern. We've gotten loads of great new stories with an army of interesting new characters.
I know lots of people think that. I'm not one of them. I was happy when only
Sinestro had a yellow ring and only
Star Sapphire had a purple one. To me, having armies of beings with rainbow colored rings is just so much, "Hey, let's just have armadas of green lanterns fighting each other for fifteen years and just use different colors to disguise our utter lack of imagination." I don't care how good some of the individual stories are. The overall premise just comes off as lazy.
I get that I'm in the minority in that opinion, but knowing that isn't going to change my mind anytime soon.