Rosario + Vampire

Rosario + Vampire (Japanese: ロザリオとバンパイア, Hepburn: Rozario to Banpaia) is a Japanese manga series written and illustrated by Akihisa Ikeda.

Plot
Tsukune Aono, a boy who's completely unable to get into any school due to his failing grades, inadvertently enrolls in a boarding school for monsters. He quickly befriends Moka Akashiya, a vampire who soon develops an obsession with his blood, and later meets other monster girls who soon take a romantic liking to him.

Why It Rocks

 * 1) While many harem animes have the girls act like they have the mentality of children and are therefore constantly taken care of and nurtured by the main male protagonist (even many of the better ones), this series is one of the few examples that doesn't adjust to that formula. As while, yes, most of the girls are pretty immature in terms of basic personality, they aren't constantly taken care of by Tsukune. On the contrary, this anime, similar to mh:awesomegames:Doki Doki Literature Club!, inverts that trope by having Moka be the one to give Tsukune the same kind of treatment.
 * 2) The art style is noticeable very nice and pleasing to look at, especially for 2000s standards.
 * 3) The concept of a school for monsters that is kept hidden from modern society is very interesting, and needless to say, it was phenomenally executed here.
 * 4) The series has a great atmosphere that perfectly fits the tone that the plot already sets up.
 * 5) All of the characters are likable and have distinct and charming personalities.
 * 6) * Tsukune Aono is a clumsy and untalented boy who was sent to Yōkai Academy due to his absolutely terrible grades having him kicked out of every other one he tried to attend, as well as the protagonist of the series.
 * 7) * Moka Akashiya is a cheerful vampire and the first (and most obvious) love interest for Tsukune. Her inner form, however, is a cold and ruthless being only kept sealed by Moka's rosary that she wears around her neck.
 * 8) * Kurumu Kurono is an arrogant and seductive succubus who is only second place to Moka in terms of popularity and originally planned to enslave all of the boys of the school with her kiss prior to falling for Tsukune.
 * 9) * Yukari Sendo is a witch who's the youngest of the main cast, as well as most of the cast at it. She's wise beyond her years and originally loathed Tsukune due to him being the centered for almost all of Moka's (some she idolizes) attention.
 * 10) * Mizore Shirayuki is a quiet Yuki-Onna who developed an obsessive crush on Tsukune after reading his news articles, to the point of stalking him.
 * 11) * Ruby Tojo is a witch who serves as an antagonist for a portion of the series. She is originally incredibly misanthropic due to a drunk driver that killed her parents in her youth, but has a change of heart after experiencing Tsukune's kindness.
 * 12) * Koko (Kokoa) Shuzen is Moka's energetic half-sister who idolizes her inner form and can be very kind and caring towards those who get to know her well.
 * 13) The characters aren't just likable, but also have great chemistry with one another. Particularly Tsukune and the girls.
 * 14) Plenty of incredibly funny moments. Such as (but certainly not limited to) Inner Moka's attempts at cooking, Kurumu chasing Mizore through the halls of Tsukune's house after an embarrassing incident in the bathroom, and Moka's expression after she's caught sucking Tsukune's blood.
 * 15) On top of the art style already being great (as previously mentions din WIR# 1), the character designs are also insanely cute. They aren't incredibly complicated, but they aren't too uncreative or boring either. For example, Mizore sports a large amount of cool colors to match the fact that she's a Yuki-Onna and Yukari wears a witch's hat and cloak, given how she's the same species.
 * 16) While a large proportion of the series isn't safe from the typical harem tropes, the series still manages to take advantage of those tropes so that they don't taint the overall narrative of the series and the books actually manages to use said tropes to it's advantage.
 * 17) The manga introduces new compelling themes and plot points as it goes on, making the plot expand more and more over the course of every book. This is best shown by how there are so many arcs in every season of the series, each one having it's own themes for their respective narratives and storylines. These also make the series deeper so that it isn't just a clumsy boy with a bunch of girls falling for him.
 * 18) There are some pretty emotional moments in the series in spite of how overall comedic tone of the manga. Such as Tsukune turning into a ghoul, Moka being kidnapped by Fairy Tale, and and Akasha's final sacrifice (which also happened to have occurred not long after her return) in the final chapter.

Bad Qualities

 * 1) While most of the series manages to utilize the standard harem cliches, it still has many of them and they can be enough to but people off the manga.
 * 2) The ending, while decent, can feel rushed or even unsatisfying to some people and could've been stronger.
 * 3) The series can get pretty mean-spirited at times, particularly in the first season where there wasn't as much plot or depth to the series and characters respectively while Tsukune and other characters are treated like punching bags.
 * 4) Tsukune, while likable, can feel like a wasted character. As while the girls are all complex in terms of their backstories and personalities, he's little more than the standard guy that attracts all of said girls.
 * 5) Despite the second season obviously being very good, it still has quite a few power ups, characters, and plot points that come out of nowhere without much (if any at all) explanation for them.
 * 6) The infamous anime adaptation.