Bloody Mary has extremely good art - if the characters are not fighting. It feels like Mary just needs to wave his hand and BAM, a mountain of vampire corpses will appear. But then the focus of Bloody Mary was never about fighting scenes, so I guess I could close an eye on that aspect.
In my opinion, Bloody Mary tries to tell a story about the will to live, the power of love (both familial & romantic love) and the meaning of forgiveness. The manga wants to deliver a profound message - but the confusing storytelling and flat side-characters mess up the process. Basically, everybody leads a tragic, torturous life because they fell in love. And everybody seems to worship or be worshipped by someone else. Characterisation is seriously lacking here, since most characters exist just for the sake of, again, worshipping or being worshipped by someone else. I am not sure if the manga is trying to follow the style of Gothic fiction - but I am sure this method of storytelling and character development (or lack thereof) is not my cup of tea.
That being said, at least the main characters, Bloody and Maria, are likeable and still function with some sort of logic. Their chemistry and occasional moments of fluff are the light that shines through this dark, twisted world of Bloody Mary. (It's not a BL by the way. At most, there are just hints of hints).
All in all, Bloody Mary was an acceptable read - at least the art is supremely well-done. Story-wise, it is not to my liking, but you may find it more satisfying than I did. This is a story about an immortal vampire that wants to die and a mortal priest that wants to live. Give it a shot if you are into vampires, Gothic world-building or BL subtext in a supernatural setting. I reckon you may enjoy it.