This was fantastic. I know I've praised the "When Wondy Was Awesome" posts a lot, but I really think this is the best. I love the story, and I don't even know where to start to praise the gorgeous art :DDD
Although, one detail bothers me... The Vesuvius thing... I live in Southern Italy, relatively close to the Vesuvius, and were it to erupt, we don't have the JL in real life. Of course this only bothers me because it strikes very close to home (literally), and not because it's an actual flaw in the story itself, so I can't really criticize it. I guess I should just grow a thicker skin.
But there is one thing I think they shouldn't have glossed over: J'onn is utterly and completely terrified of fire, so being buried alive for hours in a sea of magma should have traumatized him pretty badly. Yet that goes completely unmentioned.
How does the lasso work, exactly? I thought just touching it was enough to force one to tell the truth, yet Diana wraps it around her neck when she wants to be completely honest, and later is able to lie while carrying it.
When Batman says "flatten geneva", what does he mean? The prophecy doesn't mention any flattened country/city/thing.