What is the game about? The answer is a two part-er broken narrative and mechanic.
Narrative – The game is going to be about vampires. I know, I know what you are saying. Vampires have had a lot of play over the years, perhaps too much. There have been the gay vampires of Anne Rice, the emo goth vampires of Underworld and psycho trucker Mexican vampires from Robert Rodriguez and countless other stories. So why approach them again? What makes them interesting? It is this:

Vampires can run on the goddamn ceiling. Which leads to the main mechanic of the game.
Mechanic – The main hook of this game is going to be the ability to run on walls and ceilings. The moments in games that have always affected me the most are the ones where I am in danger of falling from a great height. Those are the moments that have produced a real world fear response in me, namely sweaty palms. The exact same reaction I have when I am near heights in real life. I want to take that fear induced response and play with it.
There have been games that let you jump off the walls or run up defined paths but never before have I ever seen a game that gives completely free reign of all six dimensions. Never has there been a game that would make your brain hurt like an MC Escher painting.

I want to play in a world where I can sprint over walls and fall up to ceilings. Where gravity is completely subjective to the player. Levels that are sprawling medieval gothic puzzles requiring fast reflexes of hand and mind.
Next up: Characters and Classes