When I first saw it I thought it as a 'Matrix meets Blade' -crossover... and only after seeing it for the second time started to think there is more in it: the mythology is very near Anne Rice's 'Interview with the Vampire' or 'Vampire: The Masqurade' (lousy series but great RPG with tons of stuff).
It was a very popular movie and a sequal is coming out - extending the mythology if we're lucky, or with too much lousy CG (if we're unlucky).