1) Hatori's author's notes are actually informative instead of self-deprecating to the point of loathing, the way that many shoujo manga artists end up writing. I actually learned quite a lot about her process and her assistants' work; it was also interesting to consider how difficult it would be to start up a story again when your artistic and storytelling skills have strengthened and progressed so much in the intervening time. She acknowledges her own failings honestly (especially the side plot regarding Chiyuki and her foster brother/cousin in Volume 2, which was just terrible) but doesn't belabor the point into "woe is me I suck" territory. All in all, a very nice read in the margins!
2) My mental summary for this series is "Twilight done right." If you're going to have a romance between a human teenager and a vampire teenager with tons of angst issues, you can't just throw in some abstinence porn and hope it works. (It really doesn't.) Instead, both of the characters need to be whole people, and this is where Millennium Snow really succeeds. Chiyuki's motivation is simple at first, since she's a young woman who's faced her own mortality from virtually the beginning of her life (due to a life-threatening heart condition), and she'd prefer some certainty that she live. But as the plot progresses and she gets to know Toya and experience life "on the outside," her motivation evolves and changes from something small and selfish into a wish that both their lives have meaning. Further, she's not just defined by her relationship to Toya or any of the other male characters. She maintains friendships and interests on her own, and her perseverance rings true, given her life experience so far. Toya, on the other hand, starts off a little one-dimensionally: the brooding teenage vampire heartthrob. (Hatori even lampshades this trope in dialogue several times, including the timeless insult, "you're stuck in a sulky pubescent funk!" leveled by the main romantic rival of the story.) But when the reasons for this brooding sulkiness are revealed, they're problems that aren't false at all; they're reasonable and right. He's asking a human woman/young adult to commit to him for at least 1,000 years, and he's thinking ahead to everything that could potentially go wrong in that time. So his reluctance to turn her plays out not as abstinence porn, but as a genuine conflict between the two characters and their desires for the future and each other. When they finally sleep together, Hatori depicts it in the sweetest, most romantic way possible, and it's just lovely.
3) It's nice to have a character in a story like this one who asks all the right questions. A new character, Kaede, is introduced in the two final volumes who functions as the group's impromptu Watcher and starts to amass as much knowledge as possible about vampires, werewolves, and other magical creatures. There's a very amusing panel at the beginning of Volume 4 where Kaede asks a long string of questions about what it's like to be a vampire or werewolf and the main characters have no answers to any of them; Kaede observes their confused conversation and thinks, "They're surprisingly ignorant..." So, like any responsible scholar, she starts to go through all the books and primary sources at hand and get some answers. If Hatori wanted to do a story about Kaede's future as a ghost hunter of some sort, I'd be there, 101%.
So I definitely recommend this series, both from an artistic standpoint (it's a great exercise in seeing someone's style evolve over time) and from a storytelling perspective. I'm very glad she didn't leave the characters dangling like that. Now I want fanfic more than ever.