If you're looking for his heart, Volthoom, you'll be sorely disappointed.
This issue begins with Guy Gardner waking up to Volthoom sucking all of the emotion out of him. While he does this, Guy Gardner experiences a double splash page with dozens of scenes from his past, both recent and Preboot. Among them are his date with Ice, his battling the Anti-Monitor (in the Sinestro Wars, it looks like. I don't think The New 52 would acknowledge Crisis on Infinite Earths!), his experiences as a police officer, his time as a Red Lantern, and his fight against The Black Lantern Corps. My favorite memory might be Bleez vomiting directly into his mouth. Sexy! Alternate versions of Guy Gardner are also shown which include his time as Warrior. So that's a healthy chunk of Preboot history that has been confirmed in The New 52.
Volthoom takes Guy Gardner on a Less Than Wonderful Life tour of how things were and how things could have been. Guy Gardner is forced to live horrible new memories which have the impact of reality since Volthoom can apparently change reality, just not permanently (yet!). Volthoom apparently feeds off of Guy's emotional peaks and valleys while toying with Guy's past.
This was my favorite comic book of the 80s: "Guy Gardner: Failure!"
Volthoom then goes to make Guy believe that he killed a bunch of Green Lanterns when he was a Red Lantern. And then his brother and sister that didn't die but now did die and the other Green Lanterns he killed but didn't kill came back as Black Lanterns to bring him down. And the issue ends with Gardner trapped in the belief of this alternate world while Volthoom feeds off of Guy's new emotional struggles. But I suppose Volthoom still can't yet change reality or else he wouldn't have to appear in New Guardians next because Kyle's brains would already have been blown out by Guy.
Green Lantern Corps #17 Rating: No change. I don't think this comic really advanced Volthoom's character or powers in this crossover. But it did add Guy Gardner Warrior to Definitive Reboot History. And if Volthoom somehow gets enough power back to actually change reality instead of just faking it and gaining power from the fakery, the DCnU is simply fucked. You think it's confusing enough right now?!