Honestly, I'm not overly fond of Nanami either. I wouldn't actually say I dislike her, but.....
I've never been able to quite pinpoint why I feel like that about her, (I do dislike those three (?) comments she makes inferring that females are inferior physically to males, but that shouldn't be enough to put me off her character. I didn't have any issues with Koizumi.)
Anyway I was thinking about it, and while I'm still not sure this is the reason behind my "coolness" to her, does anything else think that Nanami's personality (her only "negative" traits are her narcolepsy, and occasional immaturity) almost seems like it would have "fit" a little more into Dangan Ronpa 1, rather than 2.
What I mean by that is, Dangan Ronpa 1 was a little more "black and white" than 2. In Dangan Ronpa 1, hope is good. Despair is bad. Some of the students did terrible things, but you also had Chihiro, Naegi, and Taka, who were decent people without a dark past.
Then in Dangan Ronpa 2, we see that hope can be just as bad as despair when it becomes warped, and there's a constant threat throughout almost the entire game to remind us of that. Even untainted hope cannot exist without despair.
The students seem, as a whole to be much closer than those in Dangan Ronpa 1; there's more passing mention of those students no longer around, and they seem to show more concern for the well-being of the other students.
Even after case 1, several people still try to include Komaeda in group events, and show concern for him when he has the despair fever. (I wish they'd been nicer to Usami though. She really didn't deserve the treatment she got from everyone.) Look at the way Sakura was treated in Dangan Ronpa 1, and while she may have been reporting to Monokuma, she never harmed anyone.
Even with the motives; most of the Dangan Ronpa 2 cast killed for love (not counting case three of Dangan Ronpa 2 in this) or to protect another. The Dangan Ronpa 1 case killed out of a desire to escape for themselves, out of a fit of rage, or for pure greed.
And all the Dangan Ronpa 2 students, except for Nanami have done terrible things, worse (in my opinion) than what the Dangan Ronpa 1 cast did. Case 3 shows us the depths that the Ultimate Despair would go to, and even though we don't know what they all did as Ultimate Despair, we do at least know that one of them covered up a murder, and at least two of them (probably three) are murderers.
Anyway, that was long-winded, but my point was that Nanami seems almost too pure for Dangan Ronpa 2, where the story and characters are both more grey than Dangan Ronpa 1. Then again, a story such as Dangan Ronpa 2 does most likely need a pure character to act as the guiding light.