Zenphic: Retribution's campaign is generally better because it has more variety.
Aliasalpha: Say what? The retribution campaign was basically the same for every race, usually played over the same maps against the same enemies. Its certainly still worth playing but its nothing like as good as chaos rising.
Hmmm... it's been a while since I've played DoW II campaigns, so forgive me if I am mixing up the original DoW II campaign with Chaos Rising. What I remember was that there were a lot of optional missions that consisted of defending a Shrine or a factory. These missions did not further the story and, asides from the possible war gear that might be acquired, they were quite annoying.
On the other hand, Retribution had less of these kinds of missions. I was under the impression that most missions in Retribution actually furthered the story, or gave extra information about the character. That is exactly how I remember Retribution: better character development and a generally more exciting story (perhaps because of the inclusion of a new race) than the previous DoW II games.
I agree about the lackluster "choose your race" campaign. I'm disappointed that Relic went back to this style as seen in the original DoW series (Dark Crusage and Soulstorm). I'd rather have a single campaign that tells Relic's interpretation rather than multiple stories that play out almost the exact same way.