I'll start by saying I was really bummed that Maizono got offed first because she was a really intriguing character to me. Aside from her constant "psychic" joke that I was sure was bound to develop into or be revealed as something more significant later on, she was the first character who showed the most dimension (she also reminded me of June from 999, so I couldn't help but expect her to fall into a similar role). Her fears of her idol group eventually fading into obscurity and losing her friendship between them really hit home for me personally (I have a terrible habit of forming horrific futures in my mind when my life is objectively going well), and her reactions to her video (just losing all rationality of thought and sinking into despair until someone offers you some comforting words) also sort of hit home. Needless to say, I felt for her, even--no, especially when she snapped and tried to murder someone so she could graduate and get the hell out of the school to reunite with her friends as soon as possible.
I have a feeling she was sort of unstable even before going to the school, due to the overwhelming stress and pressure being an idol often costs. That said, I don't think her attachment to Naegi was all an act of manipulation, but a natural response to being brought into an unfamiliar environment and wanting to cling to the closest familiar thing possible as a security blanket. She also clearly didn't have the killer's instinct in her, as shown by her horribly failed attempt at trying to kill Kawata. This isn't to say I'm making any excuses for her actions, of course, but that I don't necessarily agree with the impression of her being manipulative in nature.
I am curious how the school trial would have gone about if she was successful, though--would she have immediately turned herself in knowing that the whole class would be executed (with emphasis on Naegi) if they didn't figure out she was the killer, or would she have continued to keep quiet about it, thinking the ends justify the means?
But enough about Maizono. Kawata! I was expecting Fukawa to be the killer based on her behavior alone (she was eager to pin the crime on Naegi and I recall her getting flustered and uncomfortable as the evidence steadily eliminated the possibility of him being hte culprit) but I'm glad I was wrong because I want to see more of her. I didn't really care about Kawata (the extra study material did little to sway my opinion of him), so I wasn't too upset he'd be gone from the cast. The way he was executed was nothing short of awful, though it does make me morbidly interested in what kind of executions will be prepared for the later murderers.
I was also bummed Enoshima got offed even before reading the extra study material, because she seemed like a fun character for the rest of the cast to play off of, and also seemed like she had more going on beneath surface impressions, and I'm glad the extra study material confirmed the latter! She was sort of similar to Maizono, but far more stable, and it's simultaneously great that Naegi was able to give her some peace of mind and horrible knowing that the fate Monobear inflicted on her amounted it to nothing.
Despite all these thoughts I have on Maizono and Enoshima, my favorite of the cast by far is Ishimaru. His over the top energy combined with his polite, formal way of speaking makes him so endearing, how can you not like the guy, if only a little?