Did you read Relic's Villains Month book? It fleshes him out quite a bit. He's nowhere near the complexity of say, Sinestro, but he's at least more interesting, and his motivations far more clear than Volthoom. I really felt Volthoom was a weak-sauce villain for the finale of such an epic run.
I've read some of his origins and I understand his motivations, but he still seems to me like a copy of Invictus in some respects. Volthoom was a more interesting antagonist to me because he has so much power and he's utterly sadistic and twisted with it, and that power makes him a more dire threat because he can harness the energy of the emotional spectrum. That's not to say Volthoom couldn't be integrated better as theenglish suggests. I'd have to read more before I can judge.