This series is for those who prefer their vampires to be cute as kittens more often than they are dark and brooding. The mood of the series, like Hazuki's personalities, tend to alternate between the two, although it generally works better when emphasizing the moe aspects, which it does a lot. That said, people with an aversion to cat-eared girls and little-sister types are advised to stay far away.
The plot tends to switch between stretches of seriousness and levity: the first two episodes deal with Hazuki meeting Kohei and escaping the castle, then settling into a silly daily routine before dealing with more villains a few episodes later. The story has some difficulty balancing character and relationship developments with plot progression unless it separates such things into different episodes. Perhaps this is why, despite several of the tragedies that various characters suffer, there is little emotional draw to them. Also, as with many adaptations of unfinished manga, a number of plot threads are left untied with the series conclusion, although the series does conclude solidly enough.
The cast are entertaining, although some people may find a number of the younger females straddle the line between adorable and irritating. Hazuki starts off as a stubborn and slightly spoiled little girl, but grows into more of a kinder, caring person over the course of the series. Kohei is the typical kind-hearted and honest but unimpressive boy with an unusual ability/curse that you've seen in so many other series. The supporting cast brings a bit of liveliness to the show. Haiji brings a bit of humor as Hazuki's cat-like pet, frequently scolding her master's servant Kohei. Seiji brings a bit of class as the cool-looking and talented relative of Kohei. The best characters, though, are probably Ryuhei and Elfriede, who regularly tease the lead characters, but also connect to each other on a deeper level and share some of the most tender moments in the series.
One can't really talk about Moon Phase without mentioning it's stylistic quirks. As with pretty much any work directed by Akiyuki Shinbo, one should expect interesting and different uses of light and color in many scenes throughout. The typical depiction of the house were much of the story occurs is also diplayed much like a dollhouse, opened up so as to see in all the rooms at once. Also, infamously, yellow washpans are known to come crashing down on various characters for comedic effect.
Designs for the characters are crisp, and backgrounds are appropriately detailed. Action scenes may not be breath-taking, but they are more than adequate for the task they mean to achieve. While the initial television episodes did have a few problems during important scenes, these were all rectified in the DVD release.
Voice work for both languages is well done, although Monica Rial can't quite match the level of cuteness that Chiwa Saito attained playing Hazuki (a minor issue). Background music for the episodes is chosen appropriately for the scene, although it is at times a little overbearing. The dark scenes are supported by haunting and gothic-sounding tones, while the cheery moments are punctuated by spunky and playful tunes. The most catchy song (for good or bad) is absolutely the opening theme, "Neko Mimi Mode De". It's particularly surprising when it drastically interrupts the gloomy introductory scene of the first episode with it's bubbly, sugary tune, simplistic lyrics, and bright colors. The song is devastatingly appropriate for the show. A couple of episodes have an alternate opening song, "Tsukuyomi Mode", that is less syrupy and not so overly energetic, but similar. The closer, on the other hand, is slightly melancholy and more subdued, but leaves little lasting impression.
Moon Phase sets out to be a vampire series built around the concept of "moe", and it largely succeeds. At times, it tries to be something a little more, and it is less definitive in its achievement when attempting this, but rarely strays far from its strength. In all, the series is an entertaining diversion for those looking for something just a little different.