I thought GASM was okay, I first rode it last September. It was really jerky, but definitely expected it. It stood out like a sore thumb though, being surrounded by those B&Ms and Intamins.
I'm not sure that Green Lantern will be a better ride....though it will be easier to maintain i'm sure. I've ridden Mantis and that's all I have to compare it to though. I'd say I liked Mantis and GASM about equal....Looks like now I've got some incentive to get back to Jackson to try it out! (As if riding El Toro again wasn't enough!)