It's been a few months since I read this, but I remember it quite well.
It was good and original... till a point. After several chapters, I just got annoyed with it. The art (I know I can't do better) was mediocre in my opinion. Then again, many mangas had this look in the past.
The story was what sold me at first, but it just seemed too dramatic and boring after awhile. The romance was one of the reasons why I just stopped loving it.
Let me just say a few words. I hate Touya... there I said it. The guy potentially being the most loved by fan girls, and I just said what any sane girl would say. (Sorry Touya fans if that comment offended you) He was too... perfect. Everyone in this manga was too flawless, excluding the villains of course. I hate characters who are brave, unselfish, and basically the definition of heroic. What makes them interesting if they don't have any quirks separating them from the rest?
The end... I won't lie to you, I just sped through because I was just frustrated and wanted to see the end. Now, I know what many will think, "You don't know if you don't read it," or something along those lines. I did read majority of it, almost forcibly.
I know it may seem like I am just only dissing this manga, so I will say a few good things that I DID like about it. I did like the idea of the plot, it was something that I had never read or heard of before. I also liked how sometimes it was sad and not happy, making it so that it seemed more realistic. (Just as a heads up, many people do die in real life, or get some other misfortune fall upon them)
Now, let's end this long review with my personal rating for each section of Ayashi No Ceres. The beginning deserves an 8, the middle of the manga deserves a 7, and the ending deserves a 6.5.
(Merely my personal opinion, others will think differently than me)