Last year I bought Tom McBride's Imperial Guard Leviathan from him. It is really a beautiful piece and of course massive. It was even the Leviathan used in the Fly Lord's of Terra's "Lords of Battle" supplement, which has rules for all those Epic and Armorcast models.
When I got it, I sent it over to Wayne Clark, my Imperial Guard painter, and he painted over the Grey with Iyaden Darksun with a Gryphon Sepia wash, just like the rest of my 15,000 points or so of IG Wayne did last year.
The datasheet is a bit weak. Here you have a colossal Doomsday Cannon with the stats of a Baneblade cannon. So the guys on the Apocalypse Forum are talking about changing the rule to S10 AP1, ignores cover saves. I think that is a closer representation of what this cannon should do.