I love Halloween and monsters but I'm not that big of a horror fan. Not going to get into that right now but a year or so ago, I found a manga that satisfies my love for Halloween without giving me nightmares. That manga is Rosario Vampire. As of the time of this post, I am 15 volumes into Rosario Vampire so this recommendation is made based on what has transpired in those volumes. I will be doing this with as little spoilers as possible.
The basic premise is that Tsukune Anno, an all around normal high school student, gets rejected from every human high school he applies to. However, he gets into the prestigious Yokai Academy, a school for monsters. At Yokai Academy, humans are killed on sight due to monsters worrying about humans finding and killing them. Fortunately for Tsukune, it is school policy for all students to maintain a human disguise. On his first day, he meets a vampire named Moka who develops quite a taste for his blood. The events that unfold in Season 1 of the manga pretty much center around Tsukune just trying to survive at the school between both in terms of his grades and fighting off students he and his friends inadvertently cross. The end of Season 1 and all of Season 2 from what I've so far is really where the things get kicked up a notch. However, the main plot of Season 1 doesn't kick in until the monstrels show up and thats where things tend to get real.
Season 2 (what I've read so far) gets really fun and its one of the main reasons why I love the characters so much particularly in regards to Mizore and Kurumu. It expands a bit on the relationship between humans and monsters while at points showing that they can sort of co-exist. This gets nicely counter-balanced by a mysterious organization known as Fairy Tale which as far as I can tell after 15 volumes seeks to either subjugate humans or at the very least is gathering its forces in case a war breaks out. That is just speculation on my part since I haven't been able to read past volume 5 of Season 2 yet.
The main cast of characters are fun and likeable.The first 5 or 6 issues of the manga are interesting in that it pulls a bit of twist with Tsukune. While he is the main character, he cannot fight on his own and usually has to rely on his monster friends to save him or have Moka give him her blood to fight. All the female characters are shown to be competent in a fight, not just Moka. I don't find any of them annoying or irritating. Mizore in particular is my favorite character and her personality plays rather well alongside Kurumu. Mizore is the typical quiet stalker chick though unlike Kurumu she isn't as forceful and actually wants Tsukune to be happy as opposed to forcing a relatioship. I'd normally find a pervy character like Gin annoying but he works out rather well since that isn't all there is to him. In Season 2, Gin's personality and history get expanded on and it makes him rather endearing. Though for some reason his dialogue gets changed to sound a bit more southern. The accent was missing in Season 1 of the manga. Koko is Moka's sister and her inferiority complex can get annoying at times but its not too bad. Kurumu's personality is interesting. She is a succubus with the power to make men fall in love with her but she wants a legitimate relationship with Tsukune despite being a bit over-zealous in her attempts. She is actually pretty innocent despite being a succubus which is weird given her mother's personality when she shows up.
The manga features the widest variety of monsters I've ever seen. It encompasses monsters from mythologies all over the world. There are even some monsters who are basically just classified as monstrels. They can basically transform their bodies into different disturbing looking weapons and those dudes are downright scary. Due to that, it leads to villains with potentially the most diverse set of powers and natures I've seen in a shonen manga. Hokuto from the end of Season 1 of the manga is my personal favorite. While his role was relatively predictable, he paints a very nice paralell with Tsukune's character. It illustrates just how badly Yokai Academy could've screwed Tsukune up if it wasn't for his friends having his back.
It is an interesting mix of genres with aspects of shonen, slight ecchi, harem, romance, and the supernatural. The ecchi aspects aren't that bad but they are rather notice-able and some of them happen often. They are quite a few panty-shots and Kurumu tends to tackle Tsukune a lot with a method I have termed the chest hug. Ruby's schtick can be a bit awkward but its fine since the main female cast tends to run the gambit of harem tropes. Any complaints I have with some of the ecchi-ness are minor complaints at best as it is more than made up for by all of the characters being like-able. With that being said, Lamia's chapter can be a bit awkwardly suggestive.
Above all else, the characters are memorable, particularly the psychotic disciplinary council who are basically only there for a couple of chapters. A lot of the one-off students/teachers are memorable as well with Lamia being one of the most memorable for the shear awkwardness she has to her. The fight scenes are intense even though Moka can end a lot of them with a single kick. My particular favorite battle was the first arc of Season 2. A doppleganger duplicated Moka's vampiric strength so the other female protagonists are nickle and dime-ing the guy until he is weak enough for Moka to finish off. Overall, the manga can be a bit generic but its enjoyable enough to overlook it. Its got its faults but I'd definitely recommend this to anyone who likes Halloween and monsters but isn't too big on horror.