To be fair, most 4x's (at least that I can recall) don't have Campaigns. MoO2, SMAC, and Gal Civ1 all did not have campaign modes, at least not for Gal Civ1 without the expansion. Now, yes, Gal Civ 2 does have a campaign, but that imposes limits on your Tech and restricts you to a map size that you cannot really control. Which is fine, it's a perfectly acceptable way to handle the campaign, it's just...I don't know, slightly odd to me.
As this is a hybrid, but with more of a RTS feel, I can understand the desire for a campaign. As I stated before, I think they could have done something cool, like expanding outwards for each "mission" instead of having discreet stages. Kinda like SupCom did it, except SupCom would move to new maps. Not sure if I'm being clear or not. Start with a small sector of space, a few planets. After a certain event (defeating pirates or something), pull back to the whole Solar System, which suddenly has invaders on a few of the outer/inner planets. As you push them back and take the star, the game pulls back even further revealing another solar system linked by the stars. All of this could be intercut with "stages" and "missions" that require a certain event to happen in order to advance the story.
I think the scores that all mention the lack of a campaign and "ding" them for it are well within their rights. After all, Perfect Scores should mean Perfect games. It's something they missed. Not that I agree with the whole number rating thing, but I understand why Sins might lose out on that.
Frankly, I look forward to seeing how Ironclad handle a sequel or expansion with a storyline included (assuming they do this).