Plot/Story
The storyline itself is very well written, with not too many typical shoujo cliches. However, as you read, you will find that a LOT of unanswered questions will pop up, with twists, turns and cliffhangers in almost every chapter. While, at first, this made the manga an extremely interesting read, it does get a little tiring as there are so many unanswered questions. Of course, I'm sure it's all to add to the suspense, but I think I'm not alone in wishing there were more answers with each chapter =d.
Characters
All the characters have quite a lot of depth, except for the main female, Yuuki Cross. She's indecisive, weak and her character isn't that substantial. Maybe the author made her this way to drag out the love triangle (i wonder if this counts as a spoiler? hmm). . . but personally, she's not really my favourite character in this manga. Zero and Kaname (main male characters), however, are brilliantly crafted into the story [if you keep my personal opinion of both of them out of this xD].
Drawing Style
Anyone who doesn't like the artwork must be blind D=<.... with bishies galore, a unique and beautiful drawing style, it all adds to the overall enjoyment factor.
Enjoyment
I love it~ what else can I say XD . . . even though I didn't give it a perfect rating =/ . . . it's still very very good. (The month wait between chapters is a little irritating, but I guess that's the same with all popular manga).
Overall
Some people may think this manga is over-rated, but to be honest, I actually read chapters 1 to 10, skipped to chapter 30, then read it again before I was hooked. It's a fantastic story, but because of its depth, some may find it a little hard to understand without reading it a couple of times, or reading discussion boards to find out what others really think of what happened in xxx chapter.