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.
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 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.