After reading volume 6, I have to say that I really enjoy the series overall.
One of the better aspects of this series is the relationships between the characters and the twisted mind battles during the special tests. It's fun how our MC has some common sense, but somehow it's kind of twisted in some weird ways. Volume 4 has some parts which shows a pretty dark side of the MC. I can't say I like him as a person, but I really appreciate how he makes the story interesting at least.
The one thing that irks me is the characterization of a certain student from the C-class. That student is almost like a plot device without any meaning other than to further the plot and an be enemy to our MC. He is to say, a lot less interesting than the other adversaries to me. Well, I hope our MC remember the promise during the end of volume 4...
I was a bit sceptical of Sudou in the beginning but he has developed into a rather interesting person along with Horikita. They really are growing on me as a couple.
He is pretty nice to Sakura, but I can't see them as a pair. Kuzuda should just disappear already. Karuizawa is the most interesting of them and I somehow ended up liking her more than I thought.