This consists of my few line comments on most characters in Kabuto. And if I skipped some characters, it simply means that I have nothing worth noting to say about them
Renge was somewhat silly, but at least she wasn't annoying (subjective opinion here). I ended up liking her quite a bit. True, she was somewhat useless after Episode 34 but I think she was the only one of Zect people who never turned against Tendou/Kabuto again after that point.
As for Tendou, I have always loved his character. I'm probably biased because I really like Hiro Mizushima. Just a little random wondering, if someone else played Tendou, would he have as good a chemistry with Yuuki Sato (Kagami) as Mizushima did? (Hey, maybe you don't think they had any chemistry, let alone a good one, but to each his/her own.)
I would rather have someone else portray Daisuke/Drake, but I think Toei made a gamble to lure in Kazuki Kato fans from the Prince of Tennis musicals. And it seemed to work. His frequent absences from the show didn't bother me as much as I found Kato to be somewhat stiff in his role. Especially when compared to Airu Kanzaki (Gon)'s excellent performance. (Sorry Kato fans, it's just my very subjective opinion. I do like some of his songs, however.)
Gon was just so great all around. She was a brat, but non-annoying one. She actually helped/bailed out Daisuke on occasions and was not simply a liability like most children in toku shows were supposed to be. (She did get kidnapped, but that was hardly her fault.) I loved Gon. And did I mention that her actress was so wonderful in her performance?
I found Tsurugi to be the most developed character. He had so many wide ranges for his actions/emotions. From being somewhat of an ass in the beginning, to being a bright eye innocent, to being friend with Kagami, to being really cool and protective of Misaki, and to being the totally final badass worm. Would love to see Yusuke Yamamoto in other stuff. Period.
Yaguruma was perfectly casted. In real life, it seems almost everyone in the Kabuto cast thinks of his actor (Hidenori Tokuyama) as an older brother.
Kageyama. Now that one is a little tough. He did a lot of backstabbings, underhanded, creepy stuff, but I had no reaction to his character whatsoever. I didn't hate him. I didn't like him. He was... just there, to kiss up to whomever. I do like his actor (Masato Uchiyama) as Ren in Ultraman Nexus though.
Irrelevant note: I slashed Yagu and Kage since Episode 8. I hadn't slashed anyone else, although I could probably see some other pairings, but it would be a bit of a stretch. Tendou/Kagami seems popular, but it is the last pairing I expect to work. And it is possible that I may have put the wrong name before the slash sign.
Riku. Now that is the way an ultimate villian (or a pretended one, as it turned out) should be portrayed. Except for the last few episodes, I really loved his character. He was so totally cool and in control. You never know what crazy thing he might do next. (He was sort of similar to Tendou, less the arrogance.)
Kagami. I don't think his character really grew up that much over the course of the series. On the bright side, for the most part I found his character's reactions to be consistant with who he was, e.g. naive, trusting, eager to please, etc.
Mishima & Negishi. Tell me again what they were doing in this show. :) Seriously, I found them to serve no purpose whatsoever. I did peg Mishima as a bad guy since day one (they weren't even subtle about this). Same with Negishi. And I found Negishi's sort of lecture to humanity to be damn condescending. Let humans sort out their own problems, worm invader!
Dark Kabuto. Poor, experimented upon kid. He was fated to die, of course, but there must be a better way for him to go out than the one on the show.
On a semi-related note, the first episode of Watashitachi no Kyoukasho, Hiro Mizushima and Shunji Igarashi's new drama, is available already as a raw, but it is a 700 meg file. I have better cleared some space on my computer.