Alright, this manga wasn't exactly what I was expecting. Judging from the first 20-30 chapters it's all about struggling to survive on an island full of vampires. After the timeskip, though, it quickly turns to actually battling the vampires and taking back the island, which is certainly an interesting turn. Let's break this down, shall we?

>Story
The story is fairly simple and easy to follow, though some moments are questionable and underwritten. For example, Pon's handgun: why did Pon, being the character that he is, never got scared to the point of using the handgun himself when he clearly should've been? Or, the student gathering for the trip to the island felt weird to me, because all the people that knew they're going to fight vampires are severely underequipped for that kind of task. I get why the rest of the students didn't bring anything to fight with, but the main characters? That seemed really weird to me. Speaking of weird, why was it necessary to, spoilers, bring the vampires from the village and Kyoko into the scene where Akira alone is supposed to show his resolve to end his brother's life? Seemed like tear-jerking for the sake of tear-jerking. But other than those three moments, nothing really stands out as a major flaw, so I'd give the story a 6/10.

>Art
The art is fantastic, nothing much to say really. I loved the artstyle the author was going for, the character design is awesome (Miyabi particularly stands out to me), disgusting scenes are actually disgusting and uncomfortable to look at, everything's as it's supposed to be. 9/10

>Characters
Alright, this is where the manga kind of falls flat in my opinion. Basically no one besides Akira gets any real character development (which is a shame since that includes most of the main cast), and the villain's motivations are unclear (at least so far). Why does he hate the humans? Why did he hate his family, besides being a wuss about how he's different from them? What happened to him that made him this way in the first place? I really hope there will be answers for these questions later in the manga, since I really like Miyabi and I think he could potentially be a great villain if the author expands on him a little bit more. Also, going back to Pon, why does Pon only serve to develop Akira as a character and not a character himself? Seems like a nitpick, but I feel like this kind of character would greatly benefit from having actual development in this kind of story with this kind of atmosphere. Nishiyama is a blank slate of a character, Katou is comic relief. The only ones who stand out to me from the main cast are Atsushi, Akira, Ken-chan and Yuki, and even then Ken-chan and Yuki are kind of questionable in that regard. Overall, I'd give the characters a 4/10.
Edit: by the end of the manga, they gave some character development to Yuki, Ken-chan and Miyabi himself, which I appreciate, so I'm willing to bump up the score to a 5/10.

>Enjoyment
Despite its' flaws, I enjoyed the manga. I really liked the atmosphere the island gave off of itself, felt really unique and interesting to me. 7/10

>Overall
For me it was an 7/10, a nice and comfy read, despite its' flaws. If you look at it objevtively it's probably a 5/10 or a 6/10, but the atmosphere and the general direction really gripped me and didn't let go. Don't know how people in the reviews give it a 1/10 or a 4/10, it clearly doesn't deserve these low scores.