So are you, dude. Which is alright; people form definite opinions on things because they think their opinions are right. That we express our opinions as facts is normal.
At any rate, I dislike the style mainly because I find it tacky.
The fact that its a cartoon look is secondary, although I think the more realistic feel of Civ V is more appropriate to the series -- Just as (btw) I think a cartoon feel was more appropriate to the Zelda series. I'm sure that could be the basis of a good discussion. I stated in an earlier comment that I think its a step back from the Civ V style aesthetically -- not technically, but aesthetically.
Of course, this is all based on the screenshots I've seen, and I don't dislike everything about it. I'll judge again when its released, and of course, even if I don't like the style, if I find the gameplay to have good enough improvements to make it worth the upgrade, I'll upgrade. I'm still skeptical about the gameplay as well, though. So I'm going to be waiting until demos. Until more comes out, I'm not that excited.
If we're getting into the technical aspects of it, as others have pointed out, there's no reason to believe they chose the style because it takes up less processing. The models seem more detailed than before, and they're adding features like day and night lighting. My experience in Civ is that most of the slowdown in late game was due to AI processing. I think it makes most sense to say the developers favored the style, for whatever reasons they had.