Let me start by saying, I enjoy story and character way above art. I didn't actually want to read this manga for a while, because I didn't like the art, but I'm glad I got over that.
I love a good heroine and I'm always on the lookout for good stories with good heroines. Yuuki starts off as an extremely average character, her nuances in the beginning are irritating, but the mangaka has taken the time to show her complexities and demonstrate why Yuuki is so indecisive, its rare to understand why a character is the way she is. Even better, the character gets over her obstacles and really begins to grow, she has slowly become one of my favourite manga females and I look forward to future growth from her.
The story has plenty of depth and subtleties for those who are willing to understand it. A warning for those who are looking for romance, even though this manga is mainly about relationships, the romance story is very slow and carefully developed and often takes a backseat to the plot.
I did have a hard time initially telling some of the characters artistically apart, but it does become pretty easy once you become used to the artist's style. I've since come to really like the art in this.
The story is very complex, there are subtleties all over the place, don't make the mistake of taking it at face value, because you'll probably only get confused and misunderstand what's going on. Do reread the story and you'll get a better understanding and appreciation. You cannot read a chapter just once, especially from chapter 35 onwards.
@asianromance - Zero & Yuuki are 1st years, the questions about the nightclass don't have any stated facts, but there are easy speculative answers to those questions.