The world in Cinder was a hella a lot exciting and intriguing than any of the actual characters (with maybe the exception of the cyborg-killing happy Doctor). Don't get me wrong, I didn't hate any of them, really, but then again I didn't really care about them much, especially Cinder and her Princey boyfriend (though her step-mother was a piece of work alright). I mean, I loved the robot more than the humans, sooo... yeah.
So yeah, the mains were pretty boring, for all that one's a cyborg in a world that hates them, and the other is the mother-effing Prince of a Commonwealth, but I liked them enough, I guess. They just didn't really have any chemistry for me, and the romance was completely and utterly bland (so bland, they alone have created a new shelf!).
But I really, really did like the world. And I'm going to read the rest for more of Meyer's vision. And more robots!
And the plot with the Lunar princess? Totally called it. I'm not sure if it was meant to be a secret or not, though. It didn't really read like a big mystery, so points off for that.