For a game like Civ 4 or that series, a campaign isn't really that important to me, and in a sense would kind of be out of place since the game spans thousands of years and takes place in a historical setting. You don't really need that much context to understand what's going on.
But in a game like this with a fantasy setting, I'm more inclined to want a campaign so that I can better immerse myself in the lore of the game and get some more context about the whole thing. There is more room for s story in a setting like this, and I'm one that likes to be told a story in an interactive medium, especially in a fantasy setting. Also, you actually have a character to role play in a game like this unlike something like Civ, and so a campaign can help with that.
Now, yes you can role play your character in the sandbox as well, and that's great too, and in fact, I'll be spending by far most of my time in the sandbox game. But if there could be a good campaign as well to help drive the story behind the world of elemental, I'm all for it and don't think it should be ignored.
Just my thoughts on the matter.