There was something about the golden forests, plains, fields, all that vivid terrain and stuff that made it feel like you were building a true utopia in Civ 5. I think the new look with the departure from realism will make it feel more like a toy world/society you're building, that would affect the atmosphere a lot and be sad I think. Especially if it's a general direction they want to drag the game, the nightmares of Spore and SimCity Societies lurk in the background (I don't think that's going to happen though, but still, no reason to approach those monsters).
But some of the new features do look nice.