Shiki is an old-fashioned vampire story with a lot of bite. If you were looking for angsty, romantic and sympathetic bloodsuckers, you may wish to look elsewhere, as this is very much a traditional horror story with nightmarish figures prowling outside (hopefully) your window. Shiki relies mainly on pyschological fright with limited but effective use of violence, but squeamish watchers should be aware that there are nevertheless scenes of intense violence, particularly towards the end of the show. For instance, the operating table scene is one of the most twisted and cruel scenes I've personally ever witnessed.
One of the interesting features of the show's story is the mixed mythologies that Shiki draws from. As well as the ghostly aspect to the undead, Ono Fuyumi obviously owes a lot to Bram Stoker, particularly with regards to the themes of class struggle and foreign invasion. The noble status of the vampires constrasts sharply with the earthy, country folk of the village and their ensuing struggle for dominance is therefore inherently political.
There are no heroes, or unamibiguous good and evil (You'll even be sympathasing with Tatsumi by the end of the story. Maybe.) in Shiki and this complex portrayal of characters is another of the show's strengths. I particularly liked the character of the village doctor, Toshio Ozaki, who to some extent personifies the famous Nietzsche quote:
"If you gaze long into an abyss, the abyss will gaze back into you."
The show isn't perfect however and one of the first things you will notice and possibly be turned off by is the artwork. I don't know what it is about the way people's hair is drawn, but it is rather ridiculous. It's almost as if everyone is an amateur scientist or wacky hair stylist who constantly experiments with static electricity to make their hair stand up. Also, the soundtrack is mainly subdued and spooky as you would expect, but the success of some of the funkier OSTs is a matter of taste.
Overall however, Shiki is well worth a look for fans of the horror genre who don't object to a fairly traditional (and to some extent predictable) vampire story. It may not be groundbreaking in any sense, but it is a well told story and the climactic last 4 episodes didn't disappoint me.