I too was surprised to discover a curve to the rings... Didn't expect that, and I'm not crazy about it. But if you don't plan to mix with other rings, it doesn't matter. And you don't really see it on the hand.
I'm not usually a fan of diamonds (no clue about them) and bought this as a gift for my mother -- also because of the appraisal value vs. purchase price, so anything would have pleased me. But I so like the way this looks on my hand, I may buy another for myself.