It's always frustrating when a movie comes so close to achieving greatness, only to stumble and eventually fall on its face right before the finish line. Okay, maybe that's a bit harsh. But I really wanted to love Byzantium and the genuinely fresh and compelling angle you took on the vampire mythos. A welcome breath of fresh air, and perhaps even a revitalizing shot to a subgenre that has been irrevocably damaged by Twilight. While Byzantium is certainly far from being a terrible movie, it is nevertheless marred by some pretty serious character issues. Which I'll get into soon.
But first, let's focus on how your initial set-up holds tremendous promise, as we learn that a vampiric mother and daughter have been on the run for centuries and have eventually found refuge in a rundown guesthouse called Byzantium. Of course, they eventually attract the attention of their mysterious pursuers. It's a dynamite premise, which brings me to my next point: pacing is one of the film's strongest suits; rather than give a massive and unwieldly info dump right at the very beginning, you allow Clara and Eleanor's backstories to unfold at a gradual pace, teasing out more and more information in a manner that consistently feels interesting and doesn't prompt the viewer to yell "Oh, just get ON with it already!" The element of mystery is also strong, with the nature of the hunters only becoming clear through flashbacks. I appreciate slow burn stories like this. They take the time to let characters breath instead of rush them through the plot and forcing them to explain everything that's happening around them. So, kudos.
Unfortunately, this is where I start to have issues. The relationship between the mother and daughter ultimately comes off as pretty flat, even though, in theory, this should be one of the most interesting aspects of the story. Clara tells everyone who will listen how devoted she is to her child, how much she'll sacrifice for her wellbeing, but very little of this is demonstrated in her actions. Outside of one key scene set in the past (and maybe the climax), she instead seems impatient, even disdainful towards Eleanor, which makes those moments considerably less complex (and considerably less interesting). A bond like this should be enforced through onscreen action, not just exposition. Though, in all fairness, Gemma Arterton gives a pretty flat performance, so maybe that explains it.
The biggest misfire in the whole movie is easily the romance between Eleanor and Frank, played by Caleb Landry Jones and his eyebrow-raising accent. Not since Twilight (last time I bring up the T-word, I promise you) has there a more inexplicable love connection between two people. Maybe you were trying to get across the idea that Eleanor is so starved for human contact after being on the move for so long that she is willing to put up with anyone. But this doesn't really make sense, considering how aloof she is towards him when they first meet. Furthermore, he does absolutely nothing to warrant her affections, even betraying her trust in a heartbeat when she confides her secret in a moment of vulnerability. What an a-hole. But, despite it all…BAM, now they're in love. Sorry, but I just don't get it.
One thing I have absolutely no qualms with is your take on vampire lore, which dispenses with many of the established "rules" that we've seen in other works of fiction. The most noticeable being that the protagonists are able to move freely during the day without bursting into flames or spontaneously emitting body-glitter. That's cool. But even more so is the notion of vampirism being akin to a religious brotherhood, complete with a unique set of gods. Perhaps the most intriguing of these Gods - and I do admire your decision to keep many of the details in the shadows - is the concept of the Nameless Saint, an entity that becomes the mirror image of those seeking eternal life.
This film is far from perfect, but it's truly admirable that you were able to put such a unique - and even occasionally thought provoking - spin on a monster-type that's suffering from a near-terminal case of pop culture fatigue.
For that reason alone I'd say this is worth recommending. Despite those last-minute stumbles.