Review of Shiki
Spoilers below: As far as being morally ambiguous and making us question humanity's place in the food chain (a la parasyte), Shiki fails on both accounts miserably. Trying to have sympathy for the vampires is immensely difficult, as most of them seem to normalize killing humans, even reveling in it fairly quickly. It's like watching a group of sadistic serial killers terrorizing a community, bragging about their deeds, and then without a semblance of self-awareness going "why don't they like us :(" when humans take action in exterminating them - if you live by the sword, you should be prepared to die by the sword. ThereIS initial reluctance to murder by new vampires, and persisting guilt in a very few, which makes the vampire organization only more vile in how they blackmail recruits into killing by threatening their living families. Only one vampire in the series managed to do the right thing by choosing to starve over murdering friends and family to survive. While Parasyte's aliens don't share human values towards life, most of Shiki's vampires have been human until recently, which makes their adjustment jarring and contrived.
Character intentions and actions are terribly developed bordering on frustratingly nonsensical. in a couple of points humans managed to incapacitate these vampires and instead of bringing them to light as evidence, they left one free to escape, and the other forgets video evidence of it until convenient at the end. The doctor's lament that people don't believe him is pretty hypocritical considering he was denying the existence of Shiki in public a few episodes ago despite already knowing of their existence. Relationships are poorly written and contrived, with multiple characters having baffling affections or friendships to another who had showed them nothing but scorn. The vampires' decisions are probably the most frustrating to watch and try to make sense of - doing a terrible job of hiding their existence by growing their numbers exponentially, repeatedly exposing themselves to humans, killing so many in a small village that it is noticeable within a month. At some point you get the feeling that they deserve to be an endangered species, disregarding that they prey on humans.
If you need a reminder that "humans can be monsters", there are way better shows out there to watch than this. If you want to watch two factions strategically fight a covert battle, there's better shows out there. If you want a reminder that "people are stupid", this might be the show for you, you'd probably feel stupid watching 22 episodes of this hoping it would have a good payoff at the end.