Although I only read Volume 1 (the rest were not available to me yet), the story seems good, but not outstanding... what is outstanding: this is a full-color manga! Every single page is rendered in bright colors, really helps to show off the blood, amongst other things.
I like this so far because the artwork is a real pleasure to look at, and the story is interesting enough to keep me going. There was not much time to develop depth but there was time to have action (fighting) and some nice H-scenes (which seamlessly fit in, this is not a hentai work or something done just for the sex, it is integral to the plot).
It sorta reminds me of the TV series Torchwood... only, in manga form or course...
Well, I will write a deeper review when more volumes are available to me.